Systems and methods for signaling buffer output information in video coding

ABSTRACT

A method of decoding video data includes receiving a first decoding unit information message corresponding to a first decoding unit of a current access unit, determining a syntax element used to compute a decoded picture buffer output time of the current access unit is not present in the first decoding unit information message, and based on the syntax element not being present in the first decoding unit information message, inferring the value of the syntax element to be equal to a value of a corresponding instance of the syntax element in a second decoding unit information message, wherein the second decoding unit information corresponds to a second decoding unit belonging to the current access unit.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority from Provisional Application No. 63/151,028, the contents of which are hereby incorporated by reference into this application.

TECHNICAL FIELD

This disclosure relates to video coding and more particularly to techniques for signaling buffering information for coded video.

BACKGROUND

Digital video capabilities can be incorporated into a wide range of devices, including digital televisions, laptop or desktop computers, tablet computers, digital recording devices, digital media players, video gaming devices, cellular telephones, including so-called smartphones, medical imaging devices, and the like. Digital video may be coded according to a video coding standard. Video coding standards define the format of a compliant bitstream encapsulating coded video data. A compliant bitstream is a data structure that may be received and decoded by a video decoding device to generate reconstructed video data. Video coding standards may incorporate video compression techniques. Examples of video coding standards include ISO/IEC MPEG-4 Visual and ITU-T H.264 (also known as ISO/IEC MPEG-4 AVC) and High-Efficiency Video Coding (HEVC). HEVC is described in High Efficiency Video Coding (HEVC), Rec. ITU-T H.265, December 2016, which is incorporated by reference, and referred to herein as ITU-T H.265. Extensions and improvements for ITU-T H.265 are currently being considered for the development of next generation video coding standards. For example, the ITU-T Video Coding Experts Group (VCEG) and ISO/IEC (Moving Picture Experts Group (MPEG) (collectively referred to as the Joint Video Exploration Team (JVET)) are working to standardized video coding technology with a compression capability that significantly exceeds that of the current HEVC standard. The Joint Exploration Model 7 (JEM 7), Algorithm Description of Joint Exploration Test Model 7 (JEM 7), ISO/IEC JTC1/SC29/WG11 Document: JVET-G1001, July 2017, Torino, IT, which is incorporated by reference herein, describes the coding features that were under coordinated test model study by the JVET as potentially enhancing video coding technology beyond the capabilities of ITU-T H.265. It should be noted that the coding features of JEM 7 are implemented in JEM reference software. As used herein, the term JEM may collectively refer to algorithms included in JEM 7 and implementations of JEM reference software. Further, in response to a “Joint Call for Proposals on Video Compression with Capabilities beyond HEVC,” jointly issued by VCEG and MPEG, multiple descriptions of video coding tools were proposed by various groups at the 10^(th) Meeting of ISO/IEC JTC1/SC29/WG11 16-20 Apr. 2018, San Diego, CA From the multiple descriptions of video coding tools, a resulting initial draft text of a video coding specification is described in “Versatile Video Coding (Draft 1),” 10^(th) Meeting of ISO/IEC JTC1/SC29/WG11 16-20 Apr. 2018, San Diego, CA, document JVET-J1001-v2, which is incorporated by reference herein, and referred to as JVET-J1001. The current development of a next generation video coding standard by the VCEG and MPEG is referred to as the Versatile Video Coding (VVC) project. “Versatile Video Coding (Draft 10),” 20th Meeting of ISO/IEC JTC1/SC29/WG11 7-16 Oct. 2020, Teleconference, document JVET-T2001-v2, which is incorporated by reference herein, and referred to as JVET-T2001, represents the current iteration of the draft text of a video coding specification corresponding to the VVC project.

Video compression techniques enable data requirements for storing and transmitting video data to be reduced. Video compression techniques may reduce data requirements by exploiting the inherent redundancies in a video sequence. Video compression techniques may sub-divide a video sequence into successively smaller portions (i.e., groups of pictures within a video sequence, a picture within a group of pictures, regions within a picture, sub-regions within regions, etc.). Intra prediction coding techniques (e.g., spatial prediction techniques within a picture) and inter prediction techniques (i.e., inter-picture techniques (temporal)) may be used to generate difference values between a unit of video data to be coded and a reference unit of video data. The difference values may be referred to as residual data. Residual data may be coded as quantized transform coefficients. Syntax elements may relate residual data and a reference coding unit (e.g., intra-prediction mode indices, and motion information). Residual data and syntax elements may be entropy coded. Entropy encoded residual data and syntax elements may be included in data structures forming a compliant bitstream.

SUMMARY

In general, this disclosure describes various techniques for coding video data. In particular, this disclosure describes techniques for signaling buffering period information for coded video data. It should be noted that although techniques of this disclosure are described with respect to ITU-T H.264, ITU-T H.265, JEM, and JVET-T2001, the techniques of this disclosure are generally applicable to video coding. For example, the coding techniques described herein may be incorporated into video coding systems, (including video coding systems based on future video coding standards) including video block structures, intra prediction techniques, inter prediction techniques, transform techniques, filtering techniques, and/or entropy coding techniques other than those included in ITU-T H.265, JEM, and JVET-T2001. Thus, reference to ITU-T H.264, ITU-T H.265, JEM, and/or JVET-T2001 is for descriptive purposes and should not be construed to limit the scope of the techniques described herein. Further, it should be noted that incorporation by reference of documents herein is for descriptive purposes and should not be construed to limit or create ambiguity with respect to terms used herein. For example, in the case where an incorporated reference provides a different definition of a term than another incorporated reference and/or as the term is used herein, the term should be interpreted in a manner that broadly includes each respective definition and/or in a manner that includes each of the particular definitions in the alternative.

In one example, a method of decoding video data comprises receiving a first decoding unit information message corresponding to a first decoding unit of a current access unit, determining a syntax element used to compute a decoded picture buffer output time of the current access unit is not present in the first decoding unit information message, and based on the syntax element not being present in the first decoding unit information message, inferring the value of the syntax element to be equal to a value of a corresponding instance of the syntax element in a second decoding unit information message, wherein the second decoding unit information corresponds to a second decoding unit belonging to the current access unit.

In one example, a device comprises one or more processors configured to receive a first decoding unit information message corresponding to a first decoding unit of a current access unit, determine a syntax element used to compute a decoded picture buffer output time of the current access unit is not present in the first decoding unit information message, and based on the syntax element not being present in the first decoding unit information message, infer the value of the syntax element to be equal to a value of a corresponding instance of the syntax element in a second decoding unit information message, wherein the second decoding unit information corresponds to a second decoding unit belonging to the current access unit.

In one example, a non-transitory computer-readable storage medium comprises instructions stored thereon that, when executed, cause one or more processors of a device to receive a first decoding unit information message corresponding to a first decoding unit of a current access unit, determine a syntax element used to compute a decoded picture buffer output time of the current access unit is not present in the first decoding unit information message, and based on the syntax element not being present in the first decoding unit information message, infer the value of the syntax element to be equal to a value of a corresponding instance of the syntax element in a second decoding unit information message, wherein the second decoding unit information corresponds to a second decoding unit belonging to the current access unit.

The details of one or more examples are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating an example of a system that may be configured to encode and decode video data according to one or more techniques of this disclosure.

FIG. 2 is a conceptual diagram illustrating coded video data and corresponding data structures according to one or more techniques of this disclosure.

FIG. 3 is a conceptual diagram illustrating a data structure encapsulating coded video data and corresponding metadata according to one or more techniques of this disclosure.

FIG. 4 is a conceptual drawing illustrating an example of components that may be included in an implementation of a system that may be configured to encode and decode video data according to one or more techniques of this disclosure.

FIG. 5 is a block diagram illustrating an example of a video encoder that may be configured to encode video data according to one or more techniques of this disclosure.

FIG. 6 is a block diagram illustrating an example of a video decoder that may be configured to decode video data according to one or more techniques of this disclosure.

DETAILED DESCRIPTION

Video content includes video sequences comprised of a series of frames (or pictures). A series of frames may also be referred to as a group of pictures (GOP). Each video frame or picture may divided into one or more regions. Regions may be defined according to a base unit (e.g., a video block) and sets of rules defining a region. For example, a rule defining a region may be that a region must be an integer number of video blocks arranged in a rectangle. Further, video blocks in a region may be ordered according to a scan pattern (e.g., a raster scan). As used herein, the term video block may generally refer to an area of a picture or may more specifically refer to the largest array of sample values that may be predictively coded, sub-divisions thereof, and/or corresponding structures. Further, the term current video block may refer to an area of a picture being encoded or decoded. A video block may be defined as an array of sample values. It should be noted that in some cases pixel values may be described as including sample values for respective components of video data, which may also be referred to as color components, (e.g., luma (Y) and chroma (Cb and Cr) components or red, green, and blue components). It should be noted that in some cases, the terms pixel value and sample value are used interchangeably. Further, in some cases, a pixel or sample may be referred to as a pel. A video sampling format, which may also be referred to as a chroma format, may define the number of chroma samples included in a video block with respect to the number of luma samples included in a video block. For example, for the 4:2:0 sampling format, the sampling rate for the luma component is twice that of the chroma components for both the horizontal and vertical directions.

A video encoder may perform predictive encoding on video blocks and sub-divisions thereof. Video blocks and sub-divisions thereof may be referred to as nodes. ITU-T H.264 specifies a macroblock including 16×16 luma samples. That is, in ITU-T H.264, a picture is segmented into macroblocks. ITU-T H.265 specifies an analogous Coding Tree Unit (CTU) structure (which may be referred to as a largest coding unit (LCU)). In ITU-T H.265, pictures are segmented into CTUs. In ITU-T H.265, for a picture, a CTU size may be set as including 16×16, 32×32, or 64×64 luma samples. In ITU-T H.265, a CTU is composed of respective Coding Tree Blocks (CTB) for each component of video data (e.g., luma (Y) and chroma (Cb and Cr). It should be noted that video having one luma component and the two corresponding chroma components may be described as having two channels, i.e., a luma channel and a chroma channel. Further, in ITU-T H.265, a CTU may be partitioned according to a quadtree (QT) partitioning structure, which results in the CTBs of the CTU being partitioned into Coding Blocks (CB). That is, in ITU-T H.265, a CTU may be partitioned into quadtree leaf nodes. According to ITU-T H.265, one luma CB together with two corresponding chroma CBs and associated syntax elements are referred to as a coding unit (CU). In ITU-T H.265, a minimum allowed size of a CB may be signaled. In ITU-T H.265, the smallest minimum allowed size of a luma CB is 8×8 luma samples. In ITU-T H.265, the decision to code a picture area using intra prediction or inter prediction is made at the CU level.

In ITU-T H.265, a CU is associated with a prediction unit structure having its root at the CU. In ITU-T H.265, prediction unit structures allow luma and chroma CBs to be split for purposes of generating corresponding reference samples. That is, in ITU-T H.265, luma and chroma CBs may be split into respective luma and chroma prediction blocks (PBs), where a PB includes a block of sample values for which the same prediction is applied. In ITU-T H.265, a CB may be partitioned into 1, 2, or 4 PBs. ITU-T H.265 supports PB sizes from 64×64 samples down to 4×4 samples. In ITU-T H.265, square PBs are supported for intra prediction, where a CB may form the PB or the CB may be split into four square PBs. In ITU-T H.265, in addition to the square PBs, rectangular PBs are supported for inter prediction, where a CB may be halved vertically or horizontally to form PBs. Further, it should be noted that in ITU-T H.265, for inter prediction, four asymmetric PB partitions are supported, where the CB is partitioned into two PBs at one quarter of the height (at the top or the bottom) or width (at the left or the right) of the CB. Intra prediction data (e.g., intra prediction mode syntax elements) or inter prediction data (e.g., motion data syntax elements) corresponding to a PB is used to produce reference and/or predicted sample values for the PB.

JEM specifies a CTU having a maximum size of 256×256 luma samples. JEM specifies a quadtree plus binary tree (QTBT) block structure. In JEM, the QTBT structure enables quadtree leaf nodes to be further partitioned by a binary tree (BT) structure. That is, in JEM, the binary tree structure enables quadtree leaf nodes to be recursively divided vertically or horizontally. In JVET-T2001, CTUs are partitioned according a quadtree plus multi-type tree (QTMT or QT+MTT) structure. The QTMT in JVET-T2001 is similar to the QTBT in JEM. However, in JVET-T2001, in addition to indicating binary splits, the multi-type tree may indicate so-called ternary (or triple tree (TT)) splits. A ternary split divides a block vertically or horizontally into three blocks. In the case of a vertical TT split, a block is divided at one quarter of its width from the left edge and at one quarter its width from the right edge and in the case of a horizontal TT split a block is at one quarter of its height from the top edge and at one quarter of its height from the bottom edge.

As described above, each video frame or picture may be divided into one or more regions. For example, according to ITU-T H.265, each video frame or picture may be partitioned to include one or more slices and further partitioned to include one or more tiles, where each slice includes a sequence of CTUs (e.g., in raster scan order) and where a tile is a sequence of CTUs corresponding to a rectangular area of a picture. It should be noted that a slice, in ITU-T H.265, is a sequence of one or more slice segments starting with an independent slice segment and containing all subsequent dependent slice segments (if any) that precede the next independent slice segment (if any). A slice segment, like a slice, is a sequence of CTUs. Thus, in some cases, the terms slice and slice segment may be used interchangeably to indicate a sequence of CTUs arranged in a raster scan order. Further, it should be noted that in ITU-T H.265, a tile may consist of CTUs contained in more than one slice and a slice may consist of CTUs contained in more than one tile. However, ITU-T H.265 provides that one or both of the following conditions shall be fulfilled: (1) All CTUs in a slice belong to the same tile; and (2) All CTUs in a tile belong to the same slice.

With respect to JVET-T2001, slices are required to consist of an integer number of complete tiles or an integer number of consecutive complete CTU rows within a tile, instead of only being required to consist of an integer number of CTUs. It should be noted that in JVET-T2001, the slice design does not include slice segments (i.e., no independent/dependent slice segments). Thus, in JVET-T2001, a picture may include a single tile, where the single tile is contained within a single slice or a picture may include multiple tiles where the multiple tiles (or CTU rows thereof) may be contained within one or more slices. In JVET-T2001, the partitioning of a picture into tiles is specified by specifying respective heights for tile rows and respective widths for tile columns. Thus, in JVET-T2001 a tile is a rectangular region of CTUs within a particular tile row and a particular tile column position. Further, it should be noted that JVET-T2001 provides where a picture may be partitioned into subpictures, where a subpicture is a rectangular region of a CTUs within a picture. The top-left CTU of a subpicture may be located at any CTU position within a picture with subpictures being constrained to include one or more slices Thus, unlike a tile, a subpicture is not necessarily limited to a particular row and column position. It should be noted that subpictures may be useful for encapsulating regions of interest within a picture and a sub-bitstream extraction process may be used to only decode and display a particular region of interest. That is, as described in further detail below, a bitstream of coded video data includes a sequence of network abstraction layer (NAL) units, where a NAL unit encapsulates coded video data, (i.e., video data corresponding to a slice of picture) or a NAL unit encapsulates metadata used for decoding video data (e.g., a parameter set) and a sub-bitstream extraction process forms a new bitstream by removing one or more NAL units from a bitstream.

FIG. 2 is a conceptual diagram illustrating an example of a picture within a group of pictures partitioned according to tiles, slices, and subpictures. It should be noted that the techniques described herein may be applicable to tiles, slices, subpictures, sub-divisions thereof and/or equivalent structures thereto. That is, the techniques described herein may be generally applicable regardless of how a picture is partitioned into regions. For example, in some cases, the techniques described herein may be applicable in cases where a tile may be partitioned into so-called bricks, where a brick is a rectangular region of CTU rows within a particular tile. Further, for example, in some cases, the techniques described herein may be applicable in cases where one or more tiles may be included in so-called tile groups, where a tile group includes an integer number of adjacent tiles. In the example illustrated in FIG. 2 , Pic₃ is illustrated as including 16 tiles (i.e., Tile₀ to Tile₁₅) and three slices (i.e., Slice₀ to Slice₂). In the example illustrated in FIG. 2 , Slice₀ includes four tiles (i.e., Tile₀ to Tile₃), Slice₁ includes eight tiles (i.e., Tile₄ to Tile₁), and Slice₂ includes four tiles (i.e., Tile₁₂ to Tile₁₅). Further, as illustrated in the example of FIG. 2 , Pic₃ is illustrated as including two subpictures (i.e., Subpicture₀ and Subpicture₁), where Subpicture₀ includes Slice₀ and Slice₁ and where Subpicture₁ includes Slice₂. As described above, subpictures may be useful for encapsulating regions of interest within a picture and a sub-bitstream extraction process may be used in order to selectively decode (and display) a region interest. For example, referring to FIG. 2 , Subpicture₀ may corresponding to an action portion of a sporting event presentation (e.g., a view of the field) and Subpicture₁ may corresponding to a scrolling banner displayed during the sporting event presentation. By using organizing a picture into subpictures in this manner, a viewer may be able to disable the display of the scrolling banner. That is, through a sub-bitstream extraction process Slice₂ NAL unit may be removed from a bitstream (and thus not decoded and/or displayed) and Slice₀ NAL unit and Slice₁ NAL unit may be decoded and displayed. The encapsulation of slices of a picture into respective NAL unit data structures and sub-bitstream extraction are described in further detail below.

For intra prediction coding, an intra prediction mode may specify the location of reference samples within a picture. In ITU-T H.265, defined possible intra prediction modes include a planar (i.e., surface fitting) prediction mode, a DC (i.e., flat overall averaging) prediction mode, and 33 angular prediction modes (predMode: 2-34). In JEM, defined possible intra-prediction modes include a planar prediction mode, a DC prediction mode, and 65 angular prediction modes. It should be noted that planar and DC prediction modes may be referred to as non-directional prediction modes and that angular prediction modes may be referred to as directional prediction modes. It should be noted that the techniques described herein may be generally applicable regardless of the number of defined possible prediction modes.

For inter prediction coding, a reference picture is determined and a motion vector (MV) identifies samples in the reference picture that are used to generate a prediction for a current video block. For example, a current video block may be predicted using reference sample values located in one or more previously coded picture(s) and a motion vector is used to indicate the location of the reference block relative to the current video block. A motion vector may describe, for example, a horizontal displacement component of the motion vector (i.e., MV_(x)), a vertical displacement component of the motion vector (i.e., MV_(y)), and a resolution for the motion vector (e.g., one-quarter pixel precision, one-half pixel precision, one-pixel precision, two-pixel precision, four-pixel precision). Previously decoded pictures, which may include pictures output before or after a current picture, may be organized into one or more to reference pictures lists and identified using a reference picture index value. Further, in inter prediction coding, uni-prediction refers to generating a prediction using sample values from a single reference picture and bi-prediction refers to generating a prediction using respective sample values from two reference pictures. That is, in uni-prediction, a single reference picture and corresponding motion vector are used to generate a prediction for a current video block and in bi-prediction, a first reference picture and corresponding first motion vector and a second reference picture and corresponding second motion vector are used to generate a prediction for a current video block. In bi-prediction, respective sample values are combined (e.g., added, rounded, and clipped, or averaged according to weights) to generate a prediction. Pictures and regions thereof may be classified based on which types of prediction modes may be utilized for encoding video blocks thereof. That is, for regions having a B type (e.g., a B slice), bi-prediction, uni-prediction, and intra prediction modes may be utilized, for regions having a P type (e.g., a P slice), uni-prediction, and intra prediction modes may be utilized, and for regions having an I type (e.g., an I slice), only intra prediction modes may be utilized. As described above, reference pictures are identified through reference indices. For example, for a P slice, there may be a single reference picture list, RefPicList0 and for a B slice, there may be a second independent reference picture list, RefPicList1, in addition to RefPicList0. It should be noted that for uni-prediction in a B slice, one of RefPicList0 or RefPicList1 may be used to generate a prediction. Further, it should be noted that during the decoding process, at the onset of decoding a picture, reference picture list(s) are generated from previously decoded pictures stored in a decoded picture buffer (DPB).

Further, a coding standard may support various modes of motion vector prediction. Motion vector prediction enables the value of a motion vector for a current video block to be derived based on another motion vector. For example, a set of candidate blocks having associated motion information may be derived from spatial neighboring blocks and temporal neighboring blocks to the current video block. Further, generated (or default) motion information may be used for motion vector prediction. Examples of motion vector prediction include advanced motion vector prediction (AMVP), temporal motion vector prediction (TMVP), so-called “merge” mode, and “skip” and “direct” motion inference. Further, other examples of motion vector prediction include advanced temporal motion vector prediction (ATMVP) and Spatial-temporal motion vector prediction (STMVP). For motion vector prediction, both a video encoder and video decoder perform the same process to derive a set of candidates. Thus, for a current video block, the same set of candidates is generated during encoding and decoding.

As described above, for inter prediction coding, reference samples in a previously coded picture are used for coding video blocks in a current picture. Previously coded pictures which are available for use as reference when coding a current picture are referred as reference pictures. It should be noted that the decoding order does not necessary correspond with the picture output order, i.e., the temporal order of pictures in a video sequence. In ITU-T H.265, when a picture is decoded it is stored to a decoded picture buffer (DPB) (which may be referred to as frame buffer, a reference buffer, a reference picture buffer, or the like). In ITU-T H.265, pictures stored to the DPB are removed from the DPB when they been output and are no longer needed for coding subsequent pictures. In ITU-T H.265, a determination of whether pictures should be removed from the DPB is invoked once per picture, after decoding a slice header, i.e., at the onset of decoding a picture. For example, referring to FIG. 2 , Pic₂ is illustrated as referencing Pic₁. Similarly, Pic₃ is illustrated as referencing Pic₀. With respect to FIG. 2 , assuming the picture number corresponds to the decoding order, the DPB would be populated as follows: after decoding Pic₀, the DPB would include {Pic₀}; at the onset of decoding Pic₁, the DPB would include {Pic₀}; after decoding Pic₁, the DPB would include {Pic₀, Pic₁}; at the onset of decoding Pic₂, the DPB would include {Pic₀, Pic₁}. Pic₂ would then be decoded with reference to Pic₁ and after decoding Pic₂, the DPB would include {Pic₀, Pic₁, Pic₂}. At the onset of decoding Pic₃, pictures Pic₀ and Pic₁ would be marked for removal from the DPB, as they are not needed for decoding Pic; (or any subsequent pictures, not shown) and assuming Pic₁ and Pic₂ have been output, the DPB would be updated to include {Pic₀}. Pic₃ would then be decoded by referencing Pic₀. The process of marking pictures for removal from a DPB may be referred to as reference picture set (RPS) management.

As described above, intra prediction data or inter prediction data is used to produce reference sample values for a block of sample values. The difference between sample values included in a current PB, or another type of picture area structure, and associated reference samples (e.g., those generated using a prediction) may be referred to as residual data. Residual data may include respective arrays of difference values corresponding to each component of video data. Residual data may be in the pixel domain. A transform, such as, a discrete cosine transform (DCT), a discrete sine transform (DST), an integer transform, a wavelet transform, or a conceptually similar transform, may be applied to an array of difference values to generate transform coefficients. It should be noted that in ITU-T H.265 and JVET-T2001, a CU is associated with a transform tree structure having its root at the CU level. The transform tree is partitioned into one or more transform units (TUs). That is, an array of difference values may be partitioned for purposes of generating transform coefficients (e.g., four 8×8 transforms may be applied to a 16×16 array of residual values). For each component of video data, such sub-divisions of difference values may be referred to as Transform Blocks (TBs). It should be noted that in some cases, a core transform and subsequent secondary transforms may be applied (in the video encoder) to generate transform coefficients. For a video decoder, the order of transforms is reversed.

A quantization process may be performed on transform coefficients or residual sample values directly (e.g., in the case, of palette coding quantization). Quantization approximates transform coefficients by amplitudes restricted to a set of specified values. Quantization essentially scales transform coefficients in order to vary the amount of data required to represent a group of transform coefficients. Quantization may include division of transform coefficients (or values resulting from the addition of an offset value to transform coefficients) by a quantization scaling factor and any associated rounding functions (e.g., rounding to the nearest integer). Quantized transform coefficients may be referred to as coefficient level values. Inverse quantization (or “dequantization”) may include multiplication of coefficient level values by the quantization scaling factor, and any reciprocal rounding or offset addition operations. It should be noted that as used herein the term quantization process in some instances may refer to division by a scaling factor to generate level values and multiplication by a scaling factor to recover transform coefficients in some instances. That is, a quantization process may refer to quantization in some cases and inverse quantization in some cases. Further, it should be noted that although in some of the examples below quantization processes are described with respect to arithmetic operations associated with decimal notation, such descriptions are for illustrative purposes and should not be construed as limiting. For example, the techniques described herein may be implemented in a device using binary operations and the like. For example, multiplication and division operations described herein may be implemented using bit shifting operations and the like.

Quantized transform coefficients and syntax elements (e.g., syntax elements indicating a coding structure for a video block) may be entropy coded according to an entropy coding technique. An entropy coding process includes coding values of syntax elements using lossless data compression algorithms. Examples of entropy coding techniques include content adaptive variable length coding (CAVLC), context adaptive binary arithmetic coding (CABAC), probability interval partitioning entropy coding (PIPE), and the like. Entropy encoded quantized transform coefficients and corresponding entropy encoded syntax elements may form a compliant bitstream that can be used to reproduce video data at a video decoder. An entropy coding process, for example, CABAC, may include performing a binarization on syntax elements. Binarization refers to the process of converting a value of a syntax element into a series of one or more bits. These bits may be referred to as “bins.” Binarization may include one or a combination of the following coding techniques: fixed length coding, unary coding, truncated unary coding, truncated Rice coding, Golomb coding, k-th order exponential Golomb coding, and Golomb-Rice coding. For example, binarization may include representing the integer value of 5 for a syntax element as 00000101 using an 8-bit fixed length binarization technique or representing the integer value of 5 as 11110 using a unary coding binarization technique. As used herein each of the terms fixed length coding, unary coding, truncated unary coding, truncated Rice coding, Golomb coding, k-th order exponential Golomb coding, and Golomb-Rice coding may refer to general implementations of these techniques and/or more specific implementations of these coding techniques. For example, a Golomb-Rice coding implementation may be specifically defined according to a video coding standard. In the example of CABAC, for a particular bin, a context provides a most probable state (MPS) value for the bin (i.e., an MPS for a bin is one of 0 or 1) and a probability value of the bin being the MPS or the least probably state (LPS). For example, a context may indicate, that the MPS of a bin is 0 and the probability of the bin being 1 is 0.3. It should be noted that a context may be determined based on values of previously coded bins including bins in the current syntax element and previously coded syntax elements. For example, values of syntax elements associated with neighboring video blocks may be used to determine a context for a current bin.

With respect to the equations used herein, the following arithmetic operators may be used:

-   -   + Addition     -   − Subtraction     -   * Multiplication, including matrix multiplication     -   x^(y) Exponentiation. Specifies x to the power of y. In other         contexts, such notation is used for superscripting not intended         for interpretation as exponentiation.     -   / Integer division with truncation of the result toward zero.         For example, 7/4 and −7/−4 are truncated to 1 and −7/4 and 7/−4         are truncated to −1.     -   ÷ Used to denote division in mathematical equations where no         truncation or rounding is intended.

$\frac{x}{y}$

-   -   Used to denote division in mathematical equations where no         truncation or rounding is intended.

Further, the following mathematical functions may be used:

-   -   Log2(x) the base-2 logarithm of x;

${{Min}\left( {x,y} \right)} = \left\{ {\begin{matrix} {x;} & {x<=y} \\ {y;} & {x > y} \end{matrix};{{{Max}\left( {x,y} \right)} = \left\{ \begin{matrix} {x;} & {x>=y} \\ {y;} & {x < y} \end{matrix} \right.}} \right.$

-   -   Ceil(x) the smallest integer greater than or equal to x.

With respect to the example syntax used herein, the following definitions of logical operators may be applied:

-   -   x && y Boolean logical “and” of x and y     -   x∥y Boolean logical “or” of x and y     -   ! Boolean logical “not”     -   x ? y: z If x is TRUE or not equal to 0, evaluates to the value         of y; otherwise, evaluates to the value of z.

Further, the following relational operators may be applied:

-   -   > Greater than     -   >= Greater than or equal to     -   < Less than     -   <= Less than or equal to     -   = Equal to     -   != Not equal to

Further, it should be noted that in the syntax descriptors used herein, the following descriptors may be applied:

-   -   b(8): byte having any pattern of bit string (8 bits). The         parsing process for this descriptor is specified by the return         value of the function read_bits(8).     -   f(n): fixed-pattern bit string using n bits written (from left         to right) with the left bit first. The parsing process for this         descriptor is specified by the return value of the function         read_bits(n).     -   se(v): signed integer 0-th order Exp-Golomb-coded syntax element         with the left bit first.     -   tb(v): truncated binary using up to maxVal bits with maxVal         defined in the semantics of the symtax element.     -   tu(v): truncated unary using up to maxVal bits with maxVal         defined in the semantics of the symtax element.     -   u(n): unsigned integer using n bits. When n is “v” in the syntax         table, the number of bits varies in a manner dependent on the         value of other syntax elements. The parsing process for this         descriptor is specified by the return value of the function         read_bits(n) interpreted as a binary representation of an         unsigned integer with most significant bit written first.     -   ue(v): unsigned integer 0-th order Exp-Golomb-coded syntax         element with the left bit first.

As described above, video content includes video sequences comprised of a series of pictures and each picture may be divided into one or more regions. In JVET-T2001, a coded representation of a picture comprises VCL NAL units of a particular layer within an AU and contains all CTUs of the picture. For example, referring again to FIG. 2 , the coded representation of Pic₃ is encapsulated in three coded slice NAL units (i.e., Slice₀ NAL unit, Slice₁ NAL unit, and Slice₂ NAL unit). It should be noted that the term video coding layer (VCL) NAL unit is used as a collective term for coded slice NAL units, i.e., VCL NAL is a collective term which includes all types of slice NAL units. As described above, and in further detail below, a NAL unit may encapsulate metadata used for decoding video data. A NAL unit encapsulating metadata used for decoding a video sequence is generally referred to as a non-VCL NAL unit. Thus, in JVET-T2001, a NAL unit may be a VCL NAL unit or a non-VCL NAL unit. It should be noted that a VCL NAL unit includes slice header data, which provides information used for decoding the particular slice. Thus, in JVET-T2001, information used for decoding video data, which may be referred to as metadata in some cases, is not limited to being included in non-VCL NAL units. JVET-T2001 provides where a picture unit (PU) is a set of NAL units that are associated with each other according to a specified classification rule, are consecutive in decoding order, and contain exactly one coded picture and where an access unit (AU) is a set of PUs that belong to different layers and contain coded pictures associated with the same time for output from the DPB. JVET-T2001 further provides where a layer is a set of VCL NAL units that all have a particular value of a layer identifier and the associated non-VCL NAL units. Further, in JVET-T2001, a PU consists of zero or one PH NAL units, one coded picture, which comprises of one or more VCL NAL units, and zero or more other non-VCL NAL units. Further, in JVET-T2001, a coded video sequence (CVS) is a sequence of AUs that consists, in decoding order, of a CVSS AU, followed by zero or more AUs that are not CVSS AUs, including all subsequent AUs up to but not including any subsequent AU that is a CVSS AU, where a coded video sequence start (CVSS) AU is an AU in which there is a PU for each layer in the CVS and the coded picture in each present picture unit is a coded layer video sequence start (CLVSS) picture. In JVET-T2001, a coded layer video sequence (CLVS) is a sequence of PUs within the same layer that consists, in decoding order, of a CLVSS PU, followed by zero or more PUs that are not CLVSS PUs, including all subsequent PUs up to but not including any subsequent PU that is a CLVSS PU. This is, in JVET-T2001, a bitstream may be described as including a sequence of AUs forming one or more CVSs.

Multi-layer video coding enables a video presentation to be decoded/displayed as a presentation corresponding to a base layer of video data and decoded/displayed one or more additional presentations corresponding to enhancement layers of video data. For example, a base layer may enable a video presentation having a basic level of quality (e.g., a High Definition rendering and/or a 30 Hz frame rate) to be presented and an enhancement layer may enable a video presentation having an enhanced level of quality (e.g., an Ultra High Definition rendering and/or a 60 Hz frame rate) to be presented. An enhancement layer may be coded by referencing a base layer. That is, for example, a picture in an enhancement layer may be coded (e.g., using inter-layer prediction techniques) by referencing one or more pictures (including scaled versions thereof) in a base layer. It should be noted that layers may also be coded independent of each other. In this case, there may not be inter-layer prediction between two layers. Each NAL unit may include an identifier indicating a layer of video data the NAL unit is associated with. As described above, a sub-bitstream extraction process may be used to only decode and display a particular region of interest of a picture. Further, a sub-bitstream extraction process may be used to only decode and display a particular layer of video. Sub-bitstream extraction may refer to a process where a device receiving a compliant or conforming bitstream forms a new compliant or conforming bitstream by discarding and/or modifying data in the received bitstream. For example, sub-bitstream extraction may be used to form a new compliant or conforming bitstream corresponding to a particular representation of video (e.g., a high quality representation).

In JVET-T2001, each of a video sequence, a GOP, a picture, a slice, and CTU may be associated with metadata that describes video coding properties and some types of metadata an encapsulated in non-VCL NAL units. JVET-T2001 defines parameters sets that may be used to describe video data and/or video coding properties. In particular, JVET-T2001 includes the following four types of parameter sets: video parameter set (VPS), sequence parameter set (SPS), picture parameter set (PPS), and adaption parameter set (APS), where a SPS applies to apply to zero or more entire CVSs, a PPS applies to zero or more entire coded pictures, a APS applies to zero or more slices, and a VPS may be optionally referenced by a SPS. A PPS applies to an individual coded picture that refers to it. In JVET-T2001, parameter sets may be encapsulated as a non-VCL NAL unit and/or may be signaled as a message. JVET-T2001 also includes a picture header (PH) which is encapsulated as a non-VCL NAL unit. In JVET-T2001, a picture header applies to all slices of a coded picture. JVET-T2001 further enables decoding capability information (DCI) and supplemental enhancement information (SEI) messages to be signaled. In JVET-T2001, DCI and SEI messages assist in processes related to decoding, display or other purposes, however, DCI and SEI messages may not be required for constructing the luma or chroma samples according to a decoding process. In JVET-T2001, DCI and SEI messages may be signaled in a bitstream using non-VCL NAL units. Further, DCI and SEI messages may be conveyed by some mechanism other than by being present in the bitstream (i.e., signaled out-of-band).

FIG. 3 illustrates an example of a bitstream including multiple CVSs, where a CVS includes AUs, and AUs include picture units. The example illustrated in FIG. 3 corresponds to an example of encapsulating the slice NAL units illustrated in the example of FIG. 2 in a bitstream. In the example illustrated in FIG. 3 , the corresponding picture unit for Pic₃ includes the three VCL NAL coded slice NAL units, i.e., Slice₀ NAL unit, Slice₁ NAL unit, and Slice₂ NAL unit and two non-VCL NAL units, i.e., a PPS NAL Unit and a PH NAL unit. It should be noted that in FIG. 3 , HEADER is a NAL unit header (i.e., not to be confused with a slice header). Further, it should be noted that in FIG. 3 , other non-VCL NAL units, which are not illustrated may be included in the CVSs, e.g., SPS NAL units, VPS NAL units, SEI message NAL units, etc. Further, it should be noted that in other examples, a PPS NAL Unit used for decoding Pic₃ may be included elsewhere in the bitstream, e.g., in the picture unit corresponding to Pic₀ or may be provided by an external mechanism. As described in further detail below, in JVET-T2001, a PH syntax structure may be present in the slice header of a VCL NAL unit or in a PH NAL unit of the current PU.

JVET-T2001 defines NAL unit header semantics that specify the type of Raw Byte Sequence Payload (RBSP) data structure included in the NAL unit. Table 1 illustrates the syntax of the NAL unit header provided in JVET-T2001.

TABLE 1 Descriptor nal_unit_header( ) {  forbidden_zero_bit f(1)  nub_reserved_zero_bit u(1)  nuh_layer_id u(6)  nal_unit_type u(5)  nuh_temporal_id_plus1 u(3) }

JVET-T2001 provides the following definitions for the respective syntax elements illustrated in Table 1.

-   -   forbidden_zero_bit shall be equal to 0.     -   nuh_reserved_zero_bit shall be equal to 0. The value 1 of         nuh_reserved_zero_bit could be specified in the future by         ITU-T|ISO/IEC. Although the value of nuh_reserved_zero_bit is         required to be equal to 0 in this version of this Specification,         decoders conforming to this version of this Specification shall         allow the value of nuh_reserved_zero_bit equal to 1 to appear in         the syntax and shall ignore (i.e. remove from the bitstream and         discard) NAL units with nuh_reserved_zero_bit equal to 1.     -   nuh_layer_id specifies the identifier of the layer to which a         VCL NAL unit belongs or the identifier of a layer to which a         non-VCL NAL unit applies. The value of nuh_layer_id shall be in         the range of 0 to 55, inclusive. Other values for nuh_layer_id         are reserved for future use by ITU-T|ISO/IEC. Although the value         of nuh_layer_id is required to be the range of 0 to 55,         inclusive, in this version of this Specification, decoders         conforming to this version of this Specification shall allow the         value of nuh_layer_id to be greater than 55 to appear in the         syntax and shall ignore (i.e. remove from the bitstream and         discard) NAL units with nuh_layer_id greater than 55.     -   The value of nuh_layer_id shall be the same for all VCL NAL         units of a coded picture. The value of nuh_layer_id of a coded         picture or a PU is the value of the nuh_layer_id of the VCL NAL         units of the coded picture or the PU.     -   When nal_unit_type is equal to PH_NUT, or FD_NUT, nuh_layer_id         shall be equal to the nub_layer_id of associated VCL NAL unit.     -   When nal_unit_type is equal to EOS_NUT, nuh_layer_id shall be         equal to one of the nuh_layer_id values of the layers present in         the CVS.     -   NOTE—The value of nuh_layer_id for DCI, OPI, VPS, AUD, and EOB         NAL units is not constrained.     -   nuh_temporal_id_plus1 minus 1 specifies a temporal identifier         for the NAL unit.     -   The value of nuh_temporal_id_plus1 shall not be equal to 0.     -   The variable TemporalId is derived as follows:         TemporalId=nuh_temporal_id_plus1−1     -   When nal_unit_type is in the range of IDR_W_RADL to RSV_RAP_11,         inclusive, TemporalId shall be equal to 0.     -   When nal_unit_type is equal to STSA_NUT and     -   vps_independent_layer_flag[GeneralLayerIdx[nuh_layer_id] ] is         equal to 1, TemporalId shall be greater than 0.     -   The value of TemporalId shall be the same for all VCL NAL units         of an AU. The value of TemporalId of a coded picture, a PU, or         an AU is the value of the TemporalId of the VCL NAL units of the         coded picture, PU, or AU. The value of TemporalId of a sublayer         representation is the greatest value of TemporalId of all VCL         NAL units in the sublayer representation.     -   The value of TemporalId for non-VCL NAL units is constrained as         follows:         -   If nal_unit_type is equal to DCI_NUT, OPI_NUT, VPS_NUT, or             SPS_NUT, TemporalId shall be equal to 0 and the TemporalId             of the AU containing the NAL unit shall be equal to 0.         -   Otherwise, if nal_unit_type is equal to PH_NUT, TemporalId             shall be equal to the TemporalId of the PU containing the             NAL unit.         -   Otherwise, if nal_unit_type is equal to EOS_NUT or EOB_NUT,             TemporalId shall be equal to 0.         -   Otherwise, if nal_unit_type is equal to AUD_NUT, FD_NUT,             PREFIX_SEI_NUT, or SUFFIX_SEI_NUT, TemporalId shall be equal             to the TemporalId of the AU containing the NAL unit.         -   Otherwise, when nal_unit_type is equal to PPS_NUT,             PREFIX_APS_NUT, or SUFFIX_APS_NUT, TemporalId shall be             greater than or equal to the TemporalId of the PU containing             the NAL unit.     -   NOTE—When the NAL unit is a non-VCL NAL unit, the value of         TemporalId is equal to the minimum value of the TemporalId         values of all AUs to which the non-VCL NAL unit applies. When         nal_unit_type is equal to PPS_NUT, PREFIX_APS_NUT, or         SUFFIX_APS_NUT, TemporalId could be greater than or equal to the         TemporalId of the containing AU, as all PPSs and APSs could be         included in the beginning of the bitstream (e.g., when they are         transported out-of-band, and the receiver places them at the         beginning of the bitstream), wherein the first coded picture has         TemporalId equal to 0.     -   nal_unit_type specifies the NAL unit type, i.e., the type of         RBSP data structure contained in the NAL unit as specified in         Table 2.     -   NAL units that have nal_unit_type in the range of UNSPEC28 . . .         UNSPEC31, inclusive, for which semantics are not specified,         shall not affect the decoding process specified in this         Specification.     -   NOTE—NAL unit types in the range of UNSPEC_28 . . . UNSPEC_31         could be used as determined by the application. No decoding         process for these values of nal_unit_type is specified in this         Specification. Since different applications might use these NAL         unit types for different purposes, particular care is expected         to be exercised in the design of encoders that generate NAL         units with these nal_unit_type values, and in the design of         decoders that interpret the content of NAL units with these         nal_unit_type values. This Specification does not define any         management for these values. These nal_unit_type values might         only be suitable for use in contexts in which “collisions” of         usage (i.e., different definitions of the meaning of the NAL         unit content for the same nal_unit_type value) are unimportant,         or not possible, or are managed—e.g., defined or managed in the         controlling application or transport specification, or by         controlling the environment in which bitstreams are distributed.     -   For purposes other than determining the amount of data in the         DUs of the bitstream (as specified in Annex C), decoders shall         ignore (remove from the bitstream and discard) the contents of         all NAL units that use reserved values of nal_unit_type.         NOTE—This requirement allows future definition of compatible         extensions to this Specification.

TABLE 2 NAL unit Name of Content of NAL unit and RBSP syntax type nal_unit_type nal_unit_type structure class  0 TRAIL_NUT Coded slice of a trailing picture or VCL subpicture* slice_layer_rbsp( )  1 STSA_NUT Coded slice of an STSA picture or VCL subpicture* slice_layer_rbsp( )  2 RADL_NUT Coded slice of a RADL, picture or subpicture* VCL slice_layer_rbsp( )  3 RASL_NUT Coded slice of a RASL picture or subpicture* VCL slice_layer_rbsp( )  4 . . . 6 RSV_VCL_4 . . . Reserved non-IRAP VCL NAL unit types VCL RSV_VCL_6  7 IDR_W_RADL Coded slice of an IDR picture or subpicture* VCL  8 IDR_N_LP slice_layer_rbsp( )  9 CRA_NUT Coded slice of a CRA picture or subpicture* VCL slice_layer_rbsp( ) 10 GDR_NUT Coded slice of a GDR picture or subpicture* VCL slice_layer_rbsp( ) 11 RSV_IRAP_11 Reserved IRAP VCL NAL unit type VCL 12 OPI_NUT Operating point information non-VCL operating_point_information_rbsp( ) 13 DCI_NUT Decoding capability information non-VCL decoding_capability_information_rbsp( ) 14 VPS_NUT Video parameter set non-VCL video_parameter_set_rbsp( ) 15 SPS_NUT Sequence parameter set non-VCL seq_parameter_set_rbsp( ) 16 PPS_NUT Picture parameter set non-VCL pic_parameter_set_rbsp( ) 17 PREFIX_APS_NUT Adaptation parameter set non-VCL 18 SUFFIX_APS_NUT adaptation_parameter_set_rbsp( ) 19 PH_NUT Picture header non-VCL picture_header_rbsp( ) 20 AUD_NUT AU delimiter non-VCL access_unit_delimiter_rbsp( ) 21 EOS_NUT End of sequence non-VCL end_of_seq_rbsp( ) 22 EOB_NUT End of bitstream non-VCL end_of_bitstream_rbsp( ) 23 PREFIX_SEI_NUT Supplemental enhancement information non-VCL 24 SUFFIX_SEI_NUT sei_rbsp( ) 25 FD_NUT Filler data non-VCL filler_data_rbsp( ) 26 RSV_NVCL_26 Reserved non-VCL NAL unit types non-VCL 27 RSV_NVCL_27 28 . . . 31 UNSPEC_28 . . . Unspecified non-VCL NAL unit types non-VCL UNSPEC_31 *indicates a property of a picture when pps_mixed_nalu_types_in_pic_flag is equal to 0 and a property of the subpicture when pps_mixed_nalu_types_in_pic_flag is equal to 1.

-   -   NOTE—A clean random access (CRA) picture may have associated         RASL or RADL pictures present in the bitstream.     -   NOTE—An instantaneous decoding refresh (IDR) picture having         nal_unit_type equal to IDR_N_LP does not have associated leading         pictures present in the bitstream. An IDR picture having         nal_unit_type equal to IDR_W_RADL does not have associated RASL         pictures present in the bitstream, but may have associated RADL         pictures in the bitstream.     -   The value of nal_unit_type shall be the same for all VCL NAL         units of a subpicture. A subpicture is referred to as having the         same NAL unit type as the VCL NAL units of the subpicture.     -   For VCL NAL units of any particular picture, the following         applies:         -   If pps_mixed_nalu_types_in_pic_flag is equal to 0, the value             of nal_unit_type shall be the same for all VCL NAL units of             a picture, and a picture or a PU is referred to as having             the same NAL unit type as the coded slice NAL units of the             picture or PU.         -   Otherwise (pps_mixed_nalu_types_in_pic_flag is equal to 1),             all of the following constraints apply:             -   The picture shall have at least two subpictures.             -   VCL NAL units of the picture shall have two or more                 different nal_unit_type values.             -   There shall be no VCL NAL unit of the picture that has                 nal_unit_type equal to GDR_NUT.             -   When a VCL NAL unit of the picture has nal_unit_type                 equal to nalUnitTypeA that is equal to IDR_W_RADL,                 IDR_N_LP, or CRA_NUT, other VCL NAL units of the picture                 shall all have nal_unit_type equal to nalUnitTypeA or                 TRAIL_NUT.     -   The value of nal_unit_type shall be the same for all pictures in         an IRAP or GDR AU.     -   When sps_video_parameter_set_id is greater than 0,         vps_max_tid_il_ref_pics_plus1 [i][j] is equal to 0 for j equal         to GeneralLayerIdx[nuh_layer_id] and any value of i in the range         of j+1 to vps_max_layers_minus1, inclusive, and         pps_mixed_nalu_types_in_pic_flag is equal to 1, the value of         nal_unit_type shall not be equal to IDR_W_RADL, IDR_N_LP, or         CRA_NUT.     -   It is a requirement of bitstream conformance that the following         constraints apply:         -   When a picture is a leading picture of an IRAP picture, it             shall be a RADL or RASL picture.         -   When a subpicture is a leading subpicture of an IRAP             subpicture, it shall be a RADL or RASL subpicture.         -   When a picture is not a leading picture of an IRAP picture,             it shall not be a RADL or RASL picture.         -   When a subpicture is not a leading subpicture of an IRAP             subpicture, it shall not be a RADL or RASL subpicture.         -   No RASL pictures shall be present in the bitstream that are             associated with an IDR picture.         -   No RASL subpictures shall be present in the bitstream that             are associated with an IDR subpicture.         -   No RADL pictures shall be present in the bitstream that are             associated with an IDR picture having nal_unit_type equal to             IDR_N_LP.             -   NOTE—It is possible to perform random access at the                 position of an IRAP AU by discarding all PUs before the                 IRAP AU (and to correctly decode the non-RASL pictures                 in the IRAP AU and all the subsequent AUs in decoding                 order), provided each parameter set is available (either                 in the bitstream or by external means not specified in                 this Specification) when it is referenced.         -   No RADL subpictures shall be present in the bitstream that             are associated with an IDR subpicture having nal_unit_type             equal to IDR_N_LP.         -   Any picture, with nuh_layer_id equal to a particular value             layerId, that precedes an IRAP picture with nuh_layer_id             equal to layerId in decoding order shall precede the IRAP             picture in output order and shall precede any RADL picture             associated with the IRAP picture in output order.         -   Any subpicture, with nuh_layer_id equal to a particular             value layerId and subpicture index equal to a particular             value subpicIdx, that precedes, in decoding order, an IRAP             subpicture with nuh_layer_id equal to layerId and subpicture             index equal to subpicIdx shall precede, in output order, the             IRAP subpicture and all its associated RADL subpictures.         -   Any picture, with nuh_layer_id equal to a particular value             layerId, that precedes a recovery point picture with             nuh_layer_id equal to layerId in decoding order shall             precede the recovery point picture in output order.         -   Any subpicture, with nuh_layer_id equal to a particular             value layerId and subpicture index equal to a particular             value subpicIdx, that precedes, in decoding order, a             subpicture with nuh_layer_id equal to layerId and subpicture             index equal to subpicIdx in a recovery point picture shall             precede that subpicture in the recovery point picture in             output order.         -   Any RASL picture associated with a CRA picture shall precede             any RADL picture associated with the CRA picture in output             order.         -   Any RASL subpicture associated with a CRA subpicture shall             precede any RADL subpicture associated with the CRA             subpicture in output order.         -   Any RASL picture, with nuh_layer_id equal to a particular             value layerId, associated with a CRA picture shall follow,             in output order, any IRAP or GDR picture with nuh_layer_id             equal to layerId that precedes the CRA picture in decoding             order.         -   Any RASL subpicture, with nuh_layer_id equal to a particular             value layerId and subpicture index equal to a particular             value subpicIdx, associated with a CRA subpicture shall             follow, in output order, any IRAP or GDR subpicture, with             nuh_layer_id equal to layerId and subpicture index equal to             subpicIdx, that precedes the CRA subpicture in decoding             order.         -   If sps_field_seq_flag is equal to 0, the following applies:             when the current picture, with nuh_layer_id equal to a             particular value layerId, is a leading picture associated             with an IRAP picture, it shall precede, in decoding order,             all non-leading pictures that are associated with the same             IRAP picture. Otherwise (sps_field_seq_flag is equal to 1),             let picA and picB be the first and the last leading             pictures, in decoding order, associated with an IRAP             picture, respectively, there shall be at most one             non-leading picture with nuh_layer_id equal to layerId             preceding picA in decoding order, and there shall be no             non-leading picture with nuh_layer_id equal to layerId             between picA and picB in decoding order.         -   If sps_field_seq_flag is equal to 0, the following applies:             when the current subpicture, with nuh_layer_id equal to a             particular value layerId and subpicture index equal to a             particular value subpicIdx, is a leading subpicture             associated with an IRAP subpicture, it shall precede, in             decoding order, all non-leading subpictures that are             associated with the same IRAP subpicture. Otherwise             (sps_field_seq_flag is equal to 1), let subpicA and subpicB             be the first and the last leading subpictures, in decoding             order, associated with an IRAP subpicture, respectively,             there shall be at most one non-leading subpicture with             nuh_layer_id equal to layerId and subpicture index equal to             subpicIdx preceding subpicA in decoding order, and there             shall be no non-leading picture with nuh_layer_id equal to             layerId and subpicture index equal to subpicIdx between picA             and picB in decoding order.

It should be noted that generally, an Intra Random Access Point (TRAP) picture is a picture that does not refer to any pictures other than itself for prediction in its decoding process. In JVET-T2001, an IRAP picture may be a clean random access (CRA) picture or an instantaneous decoder refresh (IDR) picture. In JVET-T2001, the first picture in the bitstream in decoding order must be an IRAP or a gradual decoding refresh (GDR) picture. JVET-T2001 describes the concept of a leading picture, which is a picture that precedes the associated IRAP picture in output order. JVET-T2001 further describes the concept of a trailing picture which is a non-IRAP picture that follows the associated IRAP picture in output order. Trailing pictures associated with an TRAP picture also follow the IRAP picture in decoding order. For IDR pictures, there are no trailing pictures that require reference to a picture decoded prior to the IDR picture. JVET-T2001 provides where a CRA picture may have leading pictures that follow the CRA picture in decoding order and contain inter picture prediction references to pictures decoded prior to the CRA picture. Thus, when the CRA picture is used as a random access point these leading pictures may not be decodable and are identified as random access skipped leading (RASL) pictures. The other type of picture that can follow an TRAP picture in decoding order and precede it in output order is the random access decodable leading (RADL) picture, which cannot contain references to any pictures that precede the IRAP picture in decoding order. A GDR picture, is a picture for which each VCL NAL unit has nal_unit_type equal to GDR_NUT. If the current picture is a GDR picture that is associated with a picture header which signals a syntax element recovery_poc_cnt and there is a picture picA that follows the current GDR picture in decoding order in the CLVS and that has PicOrderCntVal equal to the PicOrderCntVal of the current GDR picture plus the value of recovery_poc_cnt, the picture picA is referred to as the recovery point picture.

As described above, JVET-Q2001 enables SET messages to be signaled which assist in processes related to decoding, display or other purposes. Further, a type of SEI message for VCL HRD operations includes buffering period SEI messages. As provided in Table 2, a NAL unit may include a supplemental enhancement information (SEI) syntax structure. An sei_payload( ) syntax structure may include a buffering_period( ) syntax structure. Table 3 illustrates the bufferingperiod( ) syntax structure provided in JVET-T2001.

TABLE 3 Descriptor buffering_period( payload Size ) {  bp_nal_hrd_params_present_flag u(1)  bp_vcl_hrd_params_present_flag u(1)  bp_cpb_initial_removal_delay_length_minus1 u(5)  bp_cpb_removal_delay_length_minus1 u(5)  bp_dpb_output_delay_length_minus1 u(5)  bp_du_hrd_params_present_flag u(1)  if( bp_du_hrd_params_present_flag ) {   bp_du_cpb_removal_delay_increment_length_minus1 u(5)   bp_dpb_output_delay_du_length_minus1 u(5)   bp_du_cpb_params_in_pic_timing_sei_flag u(1)   bp_du_dpb_params_in_pic_timing_sei_flag u(1)  }  bp_concatenation_flag u(1)  bp_additional_concatenation_info_present_flag u(1)  if( bp_additional_concatenation_info_present_flag )   bp_max_initial_removal_delay_for_concatenation u(v)  bp_cpb_removal_delay_delta_minus1 u(v)  bp_max_sublayers_minus1 u(3)  if( bp_max_sublayers_minus1 > 0 )   bp_cpb_removal_delay_deltas_present_flag u(1)  if( bp_cpb_removal_delay_deltas_present_flag ) {   bp_num_cpb_removal_delay_deltas_minus1 ue(v)   for( i = 0; i <= bp_num_cpb_removal_delay_deltas_minus1; i++ )    bp_cpb_removal_delay_delta_val[ i ] u(v)  }  bp_cpb_cnt_minus1 ue(v)  if( bp_max_sublayers_minus1 > 0 )   bp_sublayer_initial_cpb_removal_delay_present_flag u(1)  for( i = ( bp_sublayer_initial_cpb_removal_delay_present_flag ?    0 : bp_max_sublayers_minus1 ); i <= bp_max_sublayers_minus1; i++ ) {   if( bp_nal_hrd_params_present_flag )    for( j = 0; j < bp_cpb_cnt_minus1 + 1; j++ ) {     bp_nal_initial_cpb_removal_delay[ i ][ j ] u(v)     bp_nal_initial_cpb_removal_offset[ i ][ j ] u(v)     if( bpu_du_hrd_params_present_flag) {      bp_nal_initial_alt_cpb_removal_delay[ i ][ j ] u(v)      bp_nal_initial_alt_cpb_removal_offset[ i ][ j ] u(v)     }    }   if( bp_vcl_hrd_params_present_flag )    for( j = 0; j < bp_cpb_cnt_minus1 + ; j++ ) {     bp_vcl_initial_cpb_removal_delay[ i ][ j ] u(v)     bp_vcl_initial_cpb_removal_offset[ i ][ j ] u(v)     if( bp_du_hrd_params_present_flag ) {      bp_vcl_initial_alt_cpb_removal_delay[ i ][ j ] u(v)      bp_vcl_initial_alt_cpb_removal_offset[ i ][ j ] u(v)     }   }  }  if( bp_max_sublayers_minus1 > 0 )   bp_sublayer_dpb_output_offsets_present_flag u(1)  if( bp_sublayer_dpb_output_offsets_present_flag )   for( i = 0; i < bp_max_sublayers_minus1; i++ )    bp_dpb_output_tid_offset[ i ] ue(v)  bp_alt_cpb_params_present_flag u(1)  if( bp_alt_cpb_params_present_flag )   bp_use_alt_cpb_params_flag u(1) }

With respect to Table 3, JVET-T2001 provides the following semantics:

-   -   A BP SEI message provides initial CPB removal delay and initial         CPB removal delay offset information for initialization of the         HRD at the position of the associated AU in decoding order.     -   When the BP SEI message is present, an AU is said to be a         notDiscardableAu when the AU has TemporalId equal to 0 and has         at least one picture that has ph_non_ref_pic_flag equal to 0         that is not a RASL or RADL picture.     -   When the current AU is not the first AU in the bitstream in         decoding order, let the AU prevNonDiscardableAu be the previous         AU in decoding order with TemporalId equal to 0 that has at         least one picture that has ph_non_ref_pic_flag equal to 0 that         is not a RASL or RADL picture.

The presence of BP SEI messages is specified as follows:

-   -   If NalHrdBpPresentFlag is equal to 1 or VclHrdBpPresentFlag is         equal to 1, the following applies for each AU in the CVS:         -   If the AU is an TRAP or GDR AU, a BP SEI message applicable             to the operation point shall be associated with the AU.         -   Otherwise, if the AU is a notDiscardableAu, a BP SET message             applicable to the operation point might or might not be             associated with the AU.         -   Otherwise, the AU shall not be associated with a BP SEI             message applicable to the operation point.     -   Otherwise (NalHrdBpPresentFlag and VclHrdBpPresentFlag are both         equal to 0), no AU in the CVS shall be associated with a BP SEI         message.     -   NOTE—For some applications, frequent presence of BP SEI messages         could be desirable (e.g., for random access at an IRAP AU or a         non-IRAP AU or for bitstream splicing).     -   bp_nal_hrd_params_present_flag equal to 1 specifies that a list         of syntax element pairs bp_nal_initial_cpb_removal_delay[i][j]         and bp_nal_initial_cpb_removal_offset[i][j] are present in the         BP SEI message. bp_nal_hrd_params_present_flag equal to 0         specifies that no syntax element pairs         bp_nal_initial_cpb_removal_delay[i][j] and         bp_nal_initial_cpb_removal_offset[i][j] are present in the BP         SEI message.     -   The value of bp_nal_hrd_params_present_flag shall be equal to         general_nal_hrd_params_present_flag.     -   bp_vcl_hrd_params_present_flag equal to 1 specifies that a list         of syntax element pairs bp_vcl_initial_cpb_removal_delay[i][j]         and bp_vcl_initial_cpb_removal_offset[i][j] are present in the         BP SEI message. bp_vcl_hrd_params_present_flag equal to 0         specifies that no syntax element pairs         bp_vcl_initial_cpb_removal_delay[i][j] and         bp_vcl_initial_cpb_removal_offset[i][j] are present in the BP         SEI message.     -   The value of bp_vcl_hrd_params_present_flag shall be equal to         general_vcl_hrd_params_present_flag.     -   bp_vcl_hrd_params_present_flag and         bp_nal_hrd_params_present_flag in a BP SEI message shall not         both be equal to 0.     -   bp_cpb_initial_removal_delay_length_minus1 plus 1 specifies the         length, in bits, of the syntax elements         bp_nal_initial_cpb_removal_delay[i][j],         bp_nal_initial_cpb_removal_offset[i][j],         bp_vcl_initial_cpb_removal_delay[i][j], and         bp_vcl_initial_cpb_removal_offset[i][j] of the BP SEI messages,         and the syntax elements         pt_nal_cpb_alt_initial_removal_delay_delta[i][j],         pt_vcl_cpb_alt_initial_removal_delay_delta[i][j],         pt_nal_cpb_alt_initial_removal_offset_delta[i][j] and         pt_vcl_cpb_alt_initial_removal_offset_delta[i][j] in the PT SEI         messages in the current BP.     -   When not present, the value of         bp_cpb_initial_removal_delay_length_minus1 is inferred to be         equal to 23.     -   bp_cpb_removal_delay_length_minus1 plus 1 specifies the length,         in bits, of the syntax elements         bp_cpb_removal_delay_delta_minus1 and         bp_cpb_removal_delay_delta_val[i] in the BP SEI message and the         syntax elements pt_cpb_removal_delay_minus1[i],         pt_nal_cpb_delay_offset[i] and pt_vcl_cpb_delay_offset[i] in the         PT SEI messages in the current BP. When not present, the value         of bp_cpb_removal_delay_length_minus1 is inferred to be equal to         23.     -   bp_dpb_output_delay_length_minus1 plus 1 specifies the length,         in bits, of the syntax elements pt_dpb_output_delay,         pt_nal_dpb_delay_offset[i] and pt_vcl_dpb_delay_offset[i] in the         PT SEI messages in the current BP. When not present, the value         of bp_dpb_output_delay_length_minus1 is inferred to be equal to         23.     -   bp_du_hrd_params_present_flag equal to 1 specifies that DU level         HRD parameters are present and the HRD can be operated at the AU         level or DU level. bp_du_hrd_params_present_flag equal to 0         specifies that DU level HRD parameters are not present and the         HRD operates at the AU level. When bp_du_hrd_params_present_flag         is not present, its value is inferred to be equal to 0.     -   The value of bp_du_hrd_params_present_flag shall be equal to         general_du_hrd_params_present_flag.     -   When bp_alt_cpb_params_present_flag is equal to 1, the value of         bp_du_hrd_params_present_flag shall be equal to 0.     -   bp_du_cpb_removal_delay_increment_length_minus1 plus 1 specifies         the length, in bits, of the         pt_du_cpb_removal_delay_increment_minus1[ ][ ] and         pt_du_common_cpb_removal_delay_increment_minus1[ ] syntax         elements of the PT SEI messages in the current BP and the         dui_du_cpb_removal_delay_increment[ ] syntax element in the DUI         SEI messages in the current BP. When not present, the value of         bp_du_cpb_removal_delay_increment_length_minus1 is inferred to         be equal to 23.     -   bp_dpb_output_delay_du_length_minus1 plus 1 specifies the         length, in bits, of the pt_dpb_output_du_delay syntax element in         the PT SEI messages in the current BP and the         dui_dpb_output_du_delay syntax element in the DUI SEI messages         in the current BP. When not present, the value of         bp_dpb_output_delay_du_length_minus1 is inferred to be equal to         23.     -   It is a requirement of bitstream conformance that all         scalable-nested and non-scalable nested BP SEI messages in a CVS         shall have the same value for each of the syntax elements         bp_cpb_initial_removal_delay_length_minus1,         bp_cpb_removal_delay_length_minus1,         bp_dpb_output_delay_length_minus1,         bp_du_cpb_removal_delay_increment_length_minus1, and         bp_dpb_output_delay_du_length_minus1.     -   bp_du_cpb_params_in_pic_timing_sei_flag equal to 1 specifies         that DU level CPB removal delay parameters are present in PT SEI         messages and no DUI SEI message is available (in the CVS or         provided through external means not specified in this         Specification). bp_du_cpb_params_in_pic_timing_sei_flag equal to         0 specifies that DU level CPB removal delay parameters are         present in DUI SEI messages and PT SEI messages do not include         DU level CPB removal delay parameters. When the         bp_du_cpb_params_in_pic_timing_sei_flag syntax element is not         present, it is inferred to be equal to 0.     -   bp_du_dpb_params_in_pic_timing_sei_flag equal to 1 specifies         that DU level DPB output delay parameters are present in PT SEI         messages and not in DUI SEI messages.         bp_du_dpb_params_in_pic_timing_sei_flag equal to 0 specifies         that DU level DPB output delay parameters are present in DUI SEI         messages and not in PT SEI messages. When the         bp_du_dpb_params_in_pic_timing_sei_flag syntax element is not         present, it is inferred to be equal to 0.     -   bp_concatenation_flag indicates, when the current AU is not the         first AU in the bitstream in decoding order, whether the nominal         CPB removal time of the current AU is determined relative to the         nominal CPB removal time of the previous AU associated with a BP         SEI message or relative to the nominal CPB removal time of the         AU prevNonDiscardableAu.     -   bp_additional_concatenation_info_present_flag equal to 1         specifies that the syntax element         bp_max_initial_removal_delay_for_concatenation is present in the         BP SEI message and the syntax element         pt_delay_for_concatenation_ensured_flag is present in the PT SEI         messages. bp_additional_concatenation_info_present_flag equal to         0 specifies that the syntax element         bp_max_initial_removal_delay_for_concatenation is not present in         the BP SET message and the syntax element         pt_delay_for_concatenation_ensured_flag is not present in the PT         SEI messages.     -   bp_max_initial_removal_delay_for_concatenation could be used         together with pt_delay_for_concatenation_ensured_flag in a PT         SEI message to identify whether the nominal removal time from         the CPB of the first AU of a following BP computed with         bp_cpb_removal_delay_delta_minus1 applies. The length of         bp_max_initial_removal_delay_for_concatenation is         bp_cpb_initial_removal_delay_length_minus1+1 bits.     -   bp_cpb_removal_delay_delta_minus1 plus 1, when the current AU is         not the first AU in the bitstream in decoding order, specifies a         CPB removal delay increment value relative to the nominal CPB         removal time of the AU prevNonDiscardableAu. The length of this         syntax element is bp_cpb_removal_delay_length_minus1+1 bits.     -   When the current AU is associated with a BP SEI message and         bp_concatenation_flag is equal to 0 and the current AU is not         the first AU in the bitstream in decoding order, it is a         requirement of bitstream conformance that the following         constraint applies:         -   If the AU prevNonDiscardableAu is not associated with a BP             SEI message, the pt_cpb_removal_delay_minus1 of the current             AU shall be equal to the pt_cpb_removal_delay_minus1 of the             AU prevNonDiscardableAu plus             bp_cpb_removal_delay_delta_minus1+1.         -   Otherwise, pt_cpb_removal_delay_minus1 shall be equal to             bp_cpb_removal_delay_delta_minus1.         -   NOTE—When the current AU is associated with a BP SEI message             and bp_concatenation_flag is equal to 1, the             pt_cpb_removal_delay_minus1 for the current AU is not used.             The constraint expressed for pt_cpb_removal_delay_minus1             could, under some circumstances, make it possible to splice             bitstreams (that use suitably-designed referencing             structures) by simply changing the value of             bp_concatenation_flag from 0 to 1 in the BP SEI message for             an TRAP or GDR AU at the splicing point. When             bp_concatenation_flag is equal to 0, the constraint             expressed for pt_cpb_removal_delay_minus1 enables the             decoder to check whether the constraint is satisfied as a             way to detect the loss of the AU prevNonDiscardableAu.     -   bp_cpb_removal_delay_deltas_present_flag equal to 1 specifies         that the BP SEI message contains CPB removal delay deltas.         bp_cpb_removal_delay_deltas_present_flag equal to 0 specifies         that no CPB removal delay deltas are present in the BP SEI         message. When not present         bp_cpb_removal_delay_deltas_present_flag is inferred to be equal         to 0.     -   bp_num_cpb_removal_delay_deltas_minus1 plus 1 specifies the         number of syntax elements bp_cpb_removal_delay_delta_val[i] in         the BP SEI message. The value of num_cpb_removal_offsets_minus1         shall be in the range of 0 to 15, inclusive.     -   bp_cpb_removal_delay_delta_val[i] specifies the i-th CPB removal         delay delta. The length of this syntax element is         bp_cpb_removal_delay_length_minus1+1 bits.     -   bp_max_sublayers_minus1 plus 1 specifies the maximum number of         temporal sublayers for which the initial CPB removal delay and         the initial CPB removal offset are indicated in the BP SEI         message. The value of bp_max_sublayers_minus1 shall be in the         range of 0 to vps_max_sublayers_minus1, inclusive.     -   bp_cpb_cnt_minus1 plus 1 specifies the number of syntax element         pairs bp_nal_initial_cpb_removal_delay[i][j] and         bp_nal_initial_cpb_removal_offset[i][j] of the i-th temporal         sublayer when bp_nal_hrd_params_present_flag is equal to 1, and         the number of syntax element pairs         bp_vcl_initial_cpb_removal_delay[i][j] and         bp_vcl_initial_cpb_removal_offset[i][j] of the i-th temporal         sublayer when bp_vcl_hrd_params_present_flag is equal to 1. The         value of bp_cpb_cnt_minus1 shall be in the range of 0 to 31,         inclusive.     -   The value of bp_cpb_cnt_minus1 shall be equal to the value of         hrd_cpb_cnt_minus1.     -   bp_sublayer_initial_cpb_removal_delay_present_flag equal to 1         specifies that initial CPB removal delay related syntax elements         are present for sublayer representation(s) in the range of 0 to         bp_max_sublayers_minus1, inclusive.         bp_sublayer_initial_cpb_removal_delay_present_flag equal to 0         specifies that initial CPB removal delay related syntax elements         are present for the bp_max_sublayers_minus1-th sublayer         representation. When not present, the value of         bp_sublayer_initial_cpb_removal_delay_present_flag is inferred         to be equal to 0.     -   bp_nal_initial_cpb_removal_delay[i][j] and         bp_nal_initial_alt_cpb_removal_delay[i][j] specify the j-th         default and alternative initial CPB removal delay for the NAL         HRD in units of a 90 kHz clock of the i-th temporal sublayer.         The length of bp_nal_initial_cpb_removal_delay[i][j] and         bp_nal_initial_alt_cpb_removal_delay[i][j] is         bp_cpb_initial_removal_delay_length_minus1+1 bits. The value of         bp_nal_initial_cpb_removal_delay[i][j] and         bp_nal_initial_alt_cpb_removal_delay[i][j] shall not be equal to         0 and shall be less than or equal to         90000*(CpbSize[i][j]÷BitRate[i][j]), the time-equivalent of the         CPB size in 90 kHz clock units. When not present, the values of         bp_nal_initial_cpb_removal_delay[i][j] and         bp_nal_initial_alt_cpb_removal_delay[i][j] are inferred to be         equal to 90000*(CpbSize[i][j]÷BitRate[i][j]).     -   bp_nal_initial_cpb_removal_offset[i][j] and         bp_nal_initial_alt_cpb_removal_offset[i][j] specify the j-th         default and alternative initial CPB removal offset of the i-th         temporal sublayer for the NAL HRD in units of a 90 kHz clock.         The length of bp_nal_initial_cpb_removal_offset[i][j] and         bp_nal_initial_alt_cpb_removal_offset[i][j] is         bp_cpb_initial_removal_delay_length_minus1+1 bits. When not         present, the values of bp_nal_initial_cpb_removal_offset[i][j]         and bp_nal_initial_alt_cpb_removal_offset[i][j] are inferred to         be equal to 0.     -   Over the entire CVS, for each value pair of i and j, the sum of         bp_nal_initial_cpb_removal_delay[i][j] and         bp_nal_initial_cpb_removal_offset[i][j] shall be constant, and         the sum of bp_nal_initial_alt_cpb_removal_delay[i][j] and         bp_nal_initial_alt_cpb_removal_offset[i][j] shall be constant.     -   bp_vcl_initial_cpb_removal_delay[i][j] and         bp_vcl_initial_alt_cpb_removal_delay[i][j] specify the j-th         default and alternative initial CPB removal delay of the i-th         temporal sublayer for the VCL HRD in units of a 90 kHz clock.         The length of bp_vcl_initial_cpb_removal_delay[i][j] and         bp_vcl_initial_alt_cpb_removal_delay[i][j] is         bp_cpb_initial_removal_delay_length_minus1+1 bits. The value of         bp_vcl_initial_cpb_removal_delay[i][j] and         bp_vcl_initial_alt_cpb_removal_delay[i][j] shall not be equal to         0 and shall be less than or equal to         90000*(CpbSize[i][j]÷BitRate[i][j]), the time-equivalent of the         CPB size in 90 kHz clock units. When not present, the values of         bp_vcl_initial_cpb_removal_delay[i][j] and         bp_vcl_initial_alt_cpb_removal_delay[i][j] are inferred to be         equal to 90000*(CpbSize[i][j]÷BitRate[i][j]).     -   bp_vcl_initial_cpb_removal_offset[i][j] and         bp_vcl_initial_alt_cpb_removal_offset[i][j] specify the j-th         default and alternative initial CPB removal offset of the i-th         temporal sublayer for the VCL HRD in units of a 90 kHz clock.         The length of bp_vcl_initial_cpb_removal_offset[i] and         bp_vcl_initial_alt_cpb_removal_offset[i][j] is         bp_cpb_initial_removal_delay_length_minus1+1 bits. When not         present, the values of bp_vcl_initial_cpb_removal_offset[i][j]         and bp_vcl_initial_alt_cpb_removal_offset[i][j] are inferred to         be equal to 0.     -   Over the entire CVS, for each value pair of i and j the sum of         bp_vcl_initial_cpb_removal_delay[i][j] and         bp_vcl_initial_cpb_removal_offset[i][j] shall be constant, and         the sum of bp_vcl_initial_alt_cpb_removal_delay[i][j] and         bp_vcl_initial_alt_cpb_removal_offset[i][j] shall be constant.     -   bp_sublayer_dpb_output_offsets_present_flag equal to 1 specifies         that DPB output time offsets are present for sublayer         representation(s) with TemporalId in the range of 0 to         bp_max_sublayers_minus1−1, inclusive.         bp_sublayer_dpb_output_offsets_present_flag equal to 0 specified         that no such DPB output time offsets are present. When not         present, the value of         bp_sublayer_dpb_output_offsets_present_flag is inferred to be         equal to 0.     -   bp_dpb_output_tid_offset[i] specifies the difference between the         DPB output times for the i-th sublayer representation and the         bp_max_sublayers_minus1-th sublayer representation. When         bp_dpb_output_tid_offset[i] is not present, it is inferred to be         equal to 0.     -   bp_alt_cpb_params_present_flag equal to 1 specifies the presence         of the syntax element bp_use_alt_cpb_params_flag in the BP SEI         message and the presence of the alternative timing information         in the PT SEI messages in the current BP. When not present, the         value of bp_alt_cpb_params_present_flag is inferred to be equal         to 0. When the associated AU is not an IRAP or GDR AU, the value         of bp_alt_cpb_params_present_flag shall be equal to 0.     -   bp_use_alt_cpb_params_flag could be used to derive the value of         UseAltCpbParamsFlag. When bp_use_alt_cpb_params_flag is not         present, it is inferred to be equal to 0.     -   When one or more of the following conditions apply,         UseAltCpbParamsFlag is set equal to 1:         -   bp_use_alt_cpb_params_flag is equal to 1.         -   When some external means not specified in this Specification             is available to set UseAltCpbParamsFlag and the value of             UseAltCpbParamsFlag is set equal to 1 by the external means.

An sei_payload( ) syntax structure may include a decoding_unit_info( ) syntax structure. Table 4 illustrates the decoding_unit_info( ) syntax structure provided in JVET-T2001.

TABLE 4 De- scrip- tor decoding_unit_info( payloadSize ) {  dui_decoding_unit_idx ue(v)  if( !bp_du_cpb_params_in_pic_timing_sei_flag )   for( i = TemporalId; i <= bp_max_sublayers_minus1; i++ ) {    if( i < bp_max_sublayers_minus1 )     dui_sublayer_delays_present_flag[ i ] u(1)    if( dui_sublayer_delays_present_flag[ i ] )     dui_du_cpb_removal_delay_increment[ i ] u(v)   }  if( !bp_du_dpb_params_in_pic_timing_sei_flag )   dui_dpb_output_du_delay_present_flag u(1)  if( dui_dpb_output_du_delay_present_flag )   dui_dpb_output_du_delay u(v) }

With respect to Table 4, JVET-T2001 provides the following semantics:

-   -   The DUI SEI message provides CPB removal delay information for         the DU associated with the SEI message.     -   The following applies for the DUI SEI message syntax and         semantics:         -   The syntax elements bp_du_hrd_params_present_flag,             bp_du_cpb_params_in_pic_timing_sei_flag,             bp_du_dpb_params_in_pic_timing_sei_flag, and             bp_dpb_output_delay_du_length_minus1 are found in the BP SEI             message that is applicable to at least one of the operation             points to which the DUI SEI message applies.         -   The bitstream (or a part thereof) refers to the bitstream             subset (or a part thereof) associated with any of the             operation points to which the DUI SEI message applies.     -   The presence of DUI SEI messages for an operation point is         specified as follows:         -   If CpbDpbDelaysPresentFlag is equal to 1,             bp_du_hrd_params_present_flag is equal to 1 and             bp_du_cpb_params_in_pic_timing_sei_flag or             bp_du_dpb_params_in_pic_timing_sei_flag is equal to 0, one             or more DUI SEI messages applicable to the operation point             shall be associated with each DU in the CVS.         -   Otherwise, in the CVS there shall be no DU that is             associated with a DUI SEI message applicable to the             operation point.     -   The set of NAL units associated with a DUI SEI message consists,         in decoding order, of the SEI NAL unit containing the DUI SEI         message and all subsequent NAL units in the AU up to but not         including any subsequent SEI NAL unit containing a DUI SEI         message with a different value of dui_decoding_unit_idx. Each DU         shall include at least one VCL NAL unit. All non-VCL NAL units         associated with a VCL NAL unit shall be included in the DU         containing the VCL NAL unit. The TemporalId in the DUI SEI         message syntax is the TemporalId of the SEI NAL unit containing         the DUI SEI message.     -   dui_decoding_unit_idx specifies the index, starting from 0, to         the list of DUs in the current AU, of the DU associated with the         DUI SEI message. The value of dui_decoding_unit_idx shall be in         the range of 0 to PicSizeInCtbsY−1, inclusive.     -   A DU identified by a particular value of duIdx includes and only         includes all NAL units associated with all DUI SEI messages that         have dui_decoding_unit_idx equal to duIdx. Such a DU is also         referred to as associated with the DUI SEI messages having         dui_decoding_unit_idx equal to duIdx. For any two DUs duA and         duB in one AU with dui_decoding_unit_idx equal to duIdxA and         duIdxB, respectively, where duIdxA is less than duIdxB, duA         shall precede duB in decoding order. A NAL unit of one DU shall         not be present, in decoding order, between any two NAL units of         another DU.     -   dui_sublayer_delays_present_flag[i] equal to 1 specifies that         dui_du_cpb_removal_delay_increment[i] is present for the         sublayer with TemporalId equal to i.         dui_sublayer_delays_present_flag[i] equal to 0 specifies that         dui_du_cpb_removal_delay_increment[i] is not present for the         sublayer with TemporalId equal to i.     -   When not present, the value of         dui_sublayer_delays_present_flag[i] is inferred to be as         follows:         -   If bp_du_cpb_params_in_pic_timing_sei_flag is equal to 0 and             i is equal to bp_max_sublayers_minus1, the value of             dui_sublayer_delays_present_flag[i] is inferred to be equal             to 1.         -   Otherwise, the value of dui_sublayer_delays_present_flag[i]             is inferred to be equal to 0.     -   dui_du_cpb_removal_delay_increment[i] specifies the duration, in         units of clock sub-ticks, between the nominal CPB times of the         last DU in decoding order in the current AU and the DU         associated with the DUI SEI message when Htid is equal to i.         This value is also used to calculate an earliest possible time         of arrival of DU data into the CPB for the HSS, as specified in         Annex C. The length of this syntax element is         bp_du_cpb_removal_delay_increment_length_minus1+1. When the DU         associated with the DUI SEI message is the last DU in the         current AU, the value of dui_du_cpb_removal_delay_increment[i]         shall be equal to 0. When dui_du_cpb_removal_delay_increment[i]         is not present for any value of i less than         bp_max_sublayers_minus1, its value is inferred to be equal to         dui_du_cpb_removal_delay_increment[bp_max_sublayers_minus1].     -   dui_dpb_output_du_delay_present_flag equal to 1 specifies the         presence of the dui_dpb_output_du_delay syntax element in the         DUI SEI message. dui_dpb_output_du_delay_present_flag equal to 0         specifies the absence of the dui_dpb_output_du_delay syntax         element in the DUI SEI message. When not present, the value of         dui_dpb_output_du_delay_present_flag is inferred to be equal to         0.     -   dui_dpb_output_du_delay is used to compute the DPB output time         of the AU when DecodingUnitHrdFlag is equal to 1 and         bp_du_dpb_params_in_pic_timing_sei_flag is equal to 0. It         specifies how many sub clock ticks to wait after removal of the         last DU in an AU from the CPB before the decoded pictures of the         AU are output from the DPB. When not present, the value of         dui_dpb_output_du_delay is inferred to be equal to         pt_dpb_output_du_delay. The length of the syntax element         dui_dpb_output_du_delay is given in bits by         bp_dpb_output_delay_du_length_minus1+1.     -   It is a requirement of bitstream conformance that all DUI SEI         messages that are associated with the same AU, apply to the same         operation point, and have         bp_du_dpb_params_in_pic_timing_sei_flag equal to 0 shall have         the same value of dui_dpb_output_du_delay.     -   The output time derived from the dui_dpb_output_du_delay of any         picture that is output from an output timing conforming decoder         shall precede the output time derived from the         dui_dpb_output_du_delay of all pictures in any subsequent CVS in         decoding order.     -   The picture output order established by the values of this         syntax element shall be the same order as established by the         values of PicOrderCntVal.     -   For pictures that are not output by the “bumping” process         because they precede, in decoding order, a CVSS AU that has         sh_no_output_of_prior_pics_flag equal to 1 or inferred to be         equal to 1, the output times derived from         dui_dpb_output_du_delay shall be increasing with increasing         value of PicOrderCntVal relative to all pictures within the same         CVS.     -   For any two pictures in the CVS, the difference between the         output times of the two pictures when DecodingUnitHrdFlag is         equal to 1 shall be identical to the same difference when         DecodingUnitHrdFlag is equal to 0.

An sei_payload( ) syntax structure may include a pic_timing( ) syntax structure. Table 5 illustrates the pic_timing( ) syntax structure provided in JVET-T2001.

TABLE 5 Descriptor pic_timing( payloadSize ) {  pt_cpb_removal_delay_minus1[ bp_max_sublayers_minus1 ] u(v)  for( i = TemporalId; i < bp_max_sublayers_minus1; i++ ) {   pt_sublayer_delays_present_flag[ i ] u(1)   if( pt_sublayer_delays_present_flag[ i ] ) {    if( bp_cpb_removal_delay_deltas_present_flag )     pt_cpb_removal_delay_delta_enabled_flag[ i ] u(1)    if( pt_cpb_removal_delay_delta_enabled_flag[ i ] ) {     if( bp_num_cpb_removal_delay_deltas_minus1 > 0 )      pt_cpb_removal_delay_delta_idx[ i ] u(v)    } else     pt_cpb_removal_delay_minus1[ i ] u(v)   }  }  pt_dpb_output_delay u(v)  if( bp_alt_cpb_params_present_flag ) {   pt_cpb_alt_timing_info_present_flag u(1)   if( pt_cpb_alt_timing_info_present_flag ) {    if( bp_nal_hrd_params_present_flag ) {     for( i = ( bp_sublayer_initial_cpb_removal_delay_present_flag ? 0 :       bp_max_sublayers_minus1 ); i <= bp_max_sublayers_minus1; i +++) {      for( j = 0; j < bp_cpb_cnt_minus + 1; j++ ) {       pt_nal_cpb_alt_initial_removal_delay_delta[ i ][ j ] u(v)       pt_nal_cpb_alt_initial_removal_offset_delta[ i ][ j ] u(v)      }      pt_nal_cpb_delay_offset[ i ] u(v)      pt_nal_dpb_delay_offset[ i ] u(v)     }    }    if( bp_vcl_hrd_params_present_flag ) {     for( i = ( bp_sublayer_initial_cpb_removal_delay_present_flag ? 0 :       bp_max_sublayers_minus1 ); i <= bp_max_sublayers_minus1; i++ ) {      for( j = 0; j < bp_cpb_cnt_minus1 + 1; j ++ ) {       pt_vcl_cpb_alt_initial_removal_delay_delta[ i ][ j ] u(v)       pt_vcl_cpb_alt_initial_removal_offset_delta[ i ][ j ] u(v)      }      pt_vcl_cpb_delay_offset[ i ] u(v)      pt_vcl_dpb_delay_offset[ i ] u(v)     }    }   }  }  if( bp_du_hrd_params_present_flag &&    bp_du_dpb_params_in_pic_timing_sei_flag )   pt_dpb_output_du_delay u(v)  if( bp_du_hrd_params_present_flag &&    bp_du_cpb_params_in_pic_timing_sei_flag ) {   pt_num_decoding_units_minus1 ue(v)   if( pt_num_decoding_units_minus1 > 0 ) {    pt_du_common_cpb_removal_delay_flag u(1)    if( pt_du_common_cpb_removal_delay_flag )     for( i = TemporalId; i <= bp_max_sublayers_minus1; i++ )      if( pt_sublayer_delays_present_flag[ i ] )       pt_du_common_cpb_removal_delay_increment_minus1[ i ] u(v)    for( i = 0; i <= pt_num_decoding_units_minus1; i++ ) {     pt_num_nalus_in_du_minus1[ i ] ue(v)     if( !pt_du_common_cpb_removal_delay_flag &&       i < pt_num_decoding_units_minus1 )      for( j = TemporalId; j <= bp_max_sublayers_minus1; j++ )       if( pt_sublayer_delays_present_flag[ j ] )        pt_du_cpb_removal_delay_increment_minus1[ i ][ j ] u(v)    }   }  }  if( bp_additional_concatenation_info_present_flag )   pt_delay_for_concatenation_ensured_flag u(1)  pt_display_elemental_periods_minus1 u(8) }

With respect to Table 5, JVET-T2001 provides the following semantics:

-   -   The PT SEI message provides CPB removal delay and DPB output         delay information for the AU associated with the SEI message.     -   If bp_nal_hrd_params_present_flag or         bp_vcl_hrd_jarams_present_flag of the BP SEI message applicable         for the current AU is equal to 1, the variable         CpbDpbDelaysPresentFlag is set equal to 1. Otherwise,         CpbDpbDelaysPresentFlag is set equal to 0.     -   The presence of PT SEI messages is specified as follows:         -   If CpbDpbDelaysPresentFlag is equal to 1, a PT SEI message             shall be associated with the current AU.         -   Otherwise (CpbDpbDelaysPresentFlag is equal to 0), there             shall not be a PT SEI message associated with the current             AU.     -   The TemporalId in the PT SEI message syntax is the TemporalId of         the SEI NAL unit containing the PT SEI message.     -   pt_cpb_removal_delay_minus1[i] plus 1 is used to calculate the         number of clock ticks between the nominal CPB removal times of         the AU associated with the PT SEI message and the preceding AU         in decoding order that contains a BP SEI message when Htid is         equal to i. This value is also used to calculate an earliest         possible time of arrival of AU data into the CPB for the HSS.         The length of pt_cpb_removal_delay_minus1[i] is         bp_cpb_removal_delay_length_minus1+1 bits.     -   pt_sublayer_delays_present_flag[i] equal to 1 specifies that         pt_cpb_removal_delay_delta_idx[i] or         pt_cpb_removal_delay_minus1[i], and         pt_du_common_cpb_removal_delay_increment_minus1[i] or         pt_du_cpb_removal_delay_increment_minus1[ ][ ] are present for         the sublayer with TemporalId equal to i.         sublayer_delays_present_flag[i] equal to 0 specifies that         neither pt_cpb_removal_delay_delta_idx[i] nor         pt_cpb_removal_delay_minus1[i] and neither         pt_du_common_cpb_removal_delay_increment_minus1[i] nor         pt_du_cpb_removal_delay_increment_minus1[ ][ ] are present for         the sublayer with TemporalId equal to i. The value of         pt_sublayer_delays_present_flag[bp_max_sublayers_minus1] is         inferred to be equal to 1. When not present, the value of         pt_sublayer_delays_present_flag[i] for any i in the range of 0         to bp_max_sublayers_minus1−1, inclusive, is inferred to be equal         to 0.     -   pt_cpb_removal_delay_delta_enabled_flag[i] equal to 1 specifies         that pt_cpb_removal_delay_delta_idx[i] is present in the PT SEI         message. pt_cpb_removal_delay_delta_enabled_flag[i] equal to 0         specifies that pt_cpb_removal_delay_delta_idx[i] is not present         in the PT SEI message. When not present, the value of         pt_cpb_removal_delay_delta_enabled_flag[i] is inferred to be         equal to 0.     -   pt_cpb_removal_delay_delta_idx[i] specifies the index of the CPB         removal delta that applies to Htid equal to i in the list of         bp_cpb_removal_delay_delta_val[j] for j ranging from 0 to         bp_num_cpb_removal_delay_deltas_minus1, inclusive. The length of         pt_cpb_removal_delay_delta_idx[i] is         Ceil(Log2(bp_num_cpb_removal_delay_deltas_minus 1+1)) bits. When         pt_cpb_removal_delay_delta_idx[i] is not present and         pt_cpb_removal_delay_delta_enabled_flag[i] is equal to 1, the         value of pt_cpb_removal_delay_delta_idx[i] is inferred to be         equal to 0.     -   The variables CpbRemovalDelayMsb[i] and CpbRemovalDelayVal[i] of         the current AU are derived as follows:         -   If the current AU is the AU that initializes the HRD,             CpbRemovalDelayMsb[i] and CpbRemovalDelayVal[i] are both set             equal to 0, and the value of cpbRemovalDelayValTmp[i] is set             equal to pt_cpb_removal_delay_minus1[i]+1.         -   Otherwise, let the AU prevNonDiscardableAu be the previous             AU in decoding order with TemporalId equal to 0 that has at             least one picture that has ph_non_ref_pic_flag equal to 0             that is not a RASL or RADL, let             prevCpbRemovalDelayMinus1[i], prevCpbRemovalDelayMsb[i], and             prevBpResetFlag be set equal to the values of             cpbRemovalDelayValTmp[i]−1, CpbRemovalDelayMsb[i], and             BpResetFlag, respectively, for the AU prevNonDiscardablAu,             and the following applies:             -   CpbRemovalDelayMsb[i] is derived as follows:

 cpbRemovalDelayValTmp[ i ] = pt_cpb_removal delay_delta_enabled_flag[ i ] ?     pt_cpb_removal_delay_minus1[ bp_max_sublayers_minus1 ] + 1 +     bp_cpb_removal_delay_delta_val[ pt_cpb_removal_delay_delta_idx[ 1 ] ] :     pt_cpb_removal_delay_minus1[ i ] + 1  if( prevBpResetFlag )    CpbRemovalDelayMsb[ i ] = 0  else if( cpbRemovalDelayValTmp[ i ] < prevCpbRemovalDelayMinus1[ i ] )    CpbRemovalDelayMsb[ i ] = prevCpbRemovalDelayMsb[ i ] +  2^(bp) ^(—) ^(cpb) ^(—) ^(removal) ^(—) ^(delay) ^(—) ^(length) ^(—) ^(minus1 + 1)  else    CpbRemovalDelayMsb[ i ] = prevCpbRemovalDelayMsb[ i ] -    CpbRemovalDelayVal is derived as follows:   if( pt_sublayer_delays_present_flag[ i ] )     CpbRemovalDelayVal[ i ] = CpbRemovalDelayMsb[ i ] +   cpbRemovalDelayValTmp[ i ]   else     CpbRemovalDelayVal[ i ] = CpbRemovalDelayVal[ i + 1 ]

-   -   The value of CpbRemovalDelayVal[i] shall be in the range of 1 to         2³², inclusive.     -   The variable AuDpbOutputDelta[i] is derived as follows:         -   AuDpbOutputDelta[i]=CpbRemovalDelayVal[i]−CpbRemovalDelayVal[bp_max_sublayers_minus1]−(i==bp_max_sublayers_minus1?             0: bp_dpb_output_tid_offset[i])     -   Where the value of bp_dpb_output_tid_offset[i] is found in the         associated BP SEI message.     -   pt_dpb_output_delay is used to compute the DPB output time of         the AU. It specifies how many clock ticks to wait after removal         of an AU from the CPB before the decoded pictures of the AU are         output from the DPB.         -   NOTE—A decoded picture is not removed from the DPB at its             output time when it is still marked as “used for short-term             reference” or “used for long-term reference”.     -   The length of pt_dpb_output_delay is         bp_dpb_output_delay_length_minus1+1 bits. When         dpb_max_dec_pic_buffering_minus1[Htid] is equal to 0, the value         of pt_dpb_output_delay shall be equal to 0.     -   The output time derived from the pt_dpb_output_delay of any         picture that is output from an output timing conforming decoder         shall precede the output time derived from the         pt_dpb_output_delay of all pictures in any subsequent CVS in         decoding order.     -   The picture output order established by the values of this         syntax element shall be the same order as established by the         values of PicOrderCntVal.     -   For pictures that are not output by the “bumping” process         because they precede, in decoding order, a CVSS AU that has         sh_no_output_of_prior_pics_flag equal to 1 or inferred to be         equal to 1, the output times derived from pt_dpb_output_delay         shall be increasing with increasing value of PicOrderCntVal         relative to all pictures within the same CVS.     -   pt_cpb_alt_timing_info_present_flag equal to 1 specifies that         the syntax elements         pt_nal_cpb_alt_initial_removal_delay_delta[i][j],         pt_nal_cpb_alt_initial_removal_offset_delta[i][j],         pt_nal_cpb_delay_offset[i], pt_nal_dpb_delay_offset[i],         pt_vcl_cpb_alt_initial_removal_delay_delta[i][j],         pt_vcl_cpb_alt_initial_removal_offset_delta[i][j],         pt_vcl_cpb_delay_offset[i], and pt_vcl_dpb_delay_offset[i] could         be present in the PT SEI message.         pt_cpb_alt_timing_info_present_flag equal to 0 specifies that         these syntax elements are not present in the PT SEI message.         When all pictures in the associated AU are RASL pictures with         pps_mixed_nalu_types_in_pic_flag equal to 0, the value of         pt_cpb_alt_timing_info_present_flag shall be equal to 0.         -   NOTE—The value of pt_cpb_alt_timing_info_present_flag could             be equal to 1 for more than one AU following an IRAP AU in             decoding order. However, the alternative timing is only             applied to the first AU that has             pt_cpb_alt_timing_info_present_flag equal to 1 and follows             the IRAP AU in decoding order.     -   pt_nal_cpb_alt_initial_removal_delay_delta[i][j] specifies the         alternative initial CPB removal delay delta for the i-th         sublayer for the j-th CPB for the NAL HRD in units of a 90 kHz         clock. The length of         pt_nal_cpb_alt_initial_removal_delay_delta[i][j] is         bp_cpb_initial_removal_delay_length_minus1+1 bits.     -   When pt_cpb_alt_timing_info_present_flag is equal to 1 and         pt_nal_cpb_alt_initial_removal_delay_delta[i][j] is not present         for any value of i less than bp_max_sublayers_minus1, its value         is inferred to be equal to 0.     -   pt_nal_cpb_alt_initial_removal_offset_delta[i][j] specifies the         alternative initial CPB removal offset delta for the i-th         sublayer for the j-th CPB for the NAL HRD in units of a 90 kHz         clock. The length of         pt_nal_cpb_alt_initial_removal_offset_delta[i][j] is         bp_cpb_initial_removal_delay_length_minus1+1 bits.     -   When pt_cpb_alt_timing_info_present_flag is equal to 1 and         pt_nal_cpb_alt_initial_removal_offset_delta[i][j] is not present         for any value of i less than bp_max_sublayers_minus1, its value         is inferred to be equal to 0.     -   pt_nal_cpb_delay_offset[i] specifies, for the i-th sublayer for         the NAL HRD, an offset to be used in the derivation of the         nominal CPB removal times of the AU associated with the PT SEI         message and of the AUs following in decoding order, when the AU         associated with the PT SEI message directly follows in decoding         order the AU associated with the BP SEI message. The length of         pt_nal_cpb_delay_offset[i] is         bp_cpb_removal_delay_length_minus1+1 bits. When not present, the         value of pt_nal_cpb_delay_offset[i] is inferred to be equal to         0.     -   pt_nal_dpb_delay_offset[i] specifies, for the i-th sublayer for         the NAL HRD, an offset to be used in the derivation of the DPB         output times of the IRAP AU associated with the BP SEI message         when the AU associated with the PT SET message directly follows         in decoding order the IRAP AU associated with the BP SEI         message. The length of pt_nal_dpb_delay_offset[i] is         bp_dpb_output_delay_length_minus1+1 bits. When not present, the         value of pt_nal_dpb_delay_offset[i] is inferred to be equal to         0.     -   pt_vcl_cpb_alt_initial_removal_delay_delta[i][j] specifies the         alternative initial CPB removal delay delta for the i-th         sublayer for the j-th CPB for the VCL HRD in units of a 90 kHz         clock. The length of         pt_vcl_cpb_alt_initial_removal_delay_delta[i][j] is         bp_cpb_initial_removal_delay_length_minus1+1 bits.     -   When pt_cpb_alt_timing_info_present_flag is equal to 1 and     -   pt_vcl_cpb_alt_initial_removal_delay_delta[i][j] is not present         for any value of i less than bp_max_sublayers_minus1, its value         is inferred to be equal to 0.     -   pt_vcl_cpb_alt_initial_removal_offset_delta[i][j] specifies the         alternative initial CPB removal offset delta for the i-th         sublayer for the j-th CPB for the VCL HRD in units of a 90 kHz         clock. The length of         pt_vcl_cpb_alt_initial_removal_offset_delta[i][j] is         bp_cpb_initial_removal_delay_length_minus1+1 bits.     -   When pt_cpb_alt_timing_info_present_flag is equal to 1 and     -   pt_vcl_cpb_alt_initial_removal_offset_delta[i][j] is not present         for any value of i less than bp_max_sublayers_minus1, its value         is inferred to be equal to 0.     -   pt_vcl_cpb_delay_offset[i] specifies, for the i-th sublayer for         the VCL HRD, an offset to be used in the derivation of the         nominal CPB removal times of the AU associated with the PT SEI         message and of the AUs following in decoding order, when the AU         associated with the PT SEI message directly follows in decoding         order the AU associated with the BP SEI message. The length of         pt_vcl_cpb_delay_offset[i] is         bp_cpb_removal_delay_length_minus1+1 bits. When not present, the         value of pt_vcl_cpb_delay_offset[i] is inferred to be equal to         0.     -   pt_vcl_dpb_delay_offset[i] specifies, for the i-th sublayer for         the VCL HRD, an offset to be used in the derivation of the DPB         output times of the IRAP AU associated with the BP SEI message         when the AU associated with the PT SEI message directly follows         in decoding order the IRAP AU associated with the BP SEI         message. The length of pt_vcl_dpb_delay_offset[i] is         bp_dpb_output_delay_length_minus1+1 bits. When not present, the         value of pt_vcl_dpb_delay_offset[i] is inferred to be equal to         0.         -   The variable BpResetFlag of the current AU is derived as             follows:         -   If the current AU is associated with a BP SEI message,             BpResetFlag is set equal to 1.         -   Otherwise, BpResetFlag is set equal to 0.     -   pt_dpb_output_du_delay is used to compute the DPB output time of         the AU when DecodingUnitHrdFlag is equal to 1. It specifies how         many sub clock ticks to wait after removal of the last DU in an         AU from the CPB before the decoded pictures of the AU are output         from the DPB.     -   The length of the syntax element pt_dpb_output_du_delay is given         in bits by bp_dpb_output_delay_du_length_minus1+1.     -   The output time derived from the pt_dpb_output_du_delay of any         picture that is output from an output timing conforming decoder         shall precede the output time derived from the         pt_dpb_output_du_delay of all pictures in any subsequent CVS in         decoding order.     -   The picture output order established by the values of this         syntax element shall be the same order as established by the         values of PicOrderCntVal.     -   For pictures that are not output by the “bumping” process         because they precede, in decoding order, a CLVSS picture that         has sh_no_output_of_prior_pics_flag equal to 1 or inferred to be         equal to 1, the output times derived from pt_dpb_output_du_delay         shall be increasing with increasing value of PicOrderCntVal         relative to all pictures within the same CVS.     -   For any two pictures in the CVS, the difference between the         output times of the two pictures when DecodingUnitHrdFlag is         equal to 1 shall be identical to the same difference when         DecodingUnitHrdFlag is equal to 0.     -   pt_num_decoding_units_minus1 plus 1 specifies the number of DUs         in the AU the PT SEI message is associated with. The value of         pt_num_decoding_units_minus1 shall be in the range of 0 to         PicSizeInCtbsY−1, inclusive.     -   pt_du_common_cpb_removal_delay_flag equal to 1 specifies that         the syntax elements         pt_du_common_cpb_removal_delay_increment_minus1[i] are present.         pt_du_common_cpb_removal_delay_flag equal to 0 specifies that         the syntax elements         pt_du_common_cpb_removal_delay_increment_minus1[i] are not         present. When not present pt_du_common_cpb_removal_delay_flag is         inferred to be equal to 0.     -   pt_du_common_cpb_removal_delay_increment_minus1[i] plus 1         specifies the duration, in units of clock sub-ticks, between the         nominal CPB removal times of any two consecutive DUs in decoding         order in the AU associated with the PT SEI message when Htid is         equal to i. This value is also used to calculate an earliest         possible time of arrival of DU data into the CPB for the HSS, as         specified in Annex C. The length of this syntax element is         bp_du_cpb_removal_delay_increment_length_minus1+1 bits.     -   When pt_du_common_cpb_removal_delay_increment_minus1[i] is not         present for any value of i less than bp_max_sublayers_minus1,         its value is inferred to be equal to         pt_du_common_cpb_removal_delay_increment_minus1[bp_max_sublayers_minus1].     -   pt_num_nalus_in_du_minus1[i] plus 1 specifies the number of NAL         units in the i-th DU of the AU the PT SEI message is associated         with. The value of pt_num_nalus_in_du_minus1[i] shall be in the         range of 0 to PicSizeInCtbsY−1, inclusive.     -   The first DU of the AU consists of the first         pt_num_nalus_in_du_minus1[0]+1 consecutive NAL units in decoding         order in the AU. The i-th (with i greater than 0) DU of the AU         consists of the pt_num_nalus_in_du_minus1[i]+1 consecutive NAL         units immediately following the last NAL unit in the previous DU         of the AU, in decoding order. There shall be at least one VCL         NAL unit in each DU. All non-VCL NAL units associated with a VCL         NAL unit shall be included in the same DU as the VCL NAL unit.     -   pt_du_cpb_removal_delay_increment_minus1[i][j] plus 1 specifies         the duration, in units of clock sub-ticks, between the nominal         CPB removal times of the (i+1)-th DU and the i-th DU, in         decoding order, in the AU associated with the PT SEI message         when Htid is equal to j. This value is also used to calculate an         earliest possible time of arrival of DU data into the CPB for         the HSS, as specified in Annex C. The length of this syntax         element is bp_du_cpb_removal_delay_increment_length_minus1+1         bits.     -   When pt_du_cpb_removal_delay_increment_minus1[i][j] is not         present for any value of j less than bp_max_sublayers_minus1,         its value is inferred to be equal to         pt_du_cpb_removal_delay_increment_minus1[i][bp_max_sublayers_minus1].     -   pt_delay_for_concatenation_ensured_flag equal to 1 specifies         that the difference between the final arrival time and the CPB         removal time of the AU associated with the PT SEI message is         such that when followed by an AU with a BP SEI message with         bp_concatenation_flag equal to 1 and InitCpbRemovalDelay[ScIdx]         less than or equal to the value of         bp_max_initial_removal_delay_for_concatenation, the nominal         removal time of the following AU from the CPB computed with         bp_cpb_removal_delay_delta_minus1 applies.         pt_delay_for_concatenation_ensured_flag equal to 0 specifies         that the difference between the final arrival time and the CPB         removal time of the AU associated with the PT SEI message might         or might not exceed the value of         max_val_initial_removal_delay_for_splicing.     -   pt_display_elemental_periods_minus1 plus 1, when         sps_field_seq_flag is equal to 0 and         fixed_pic_rate_within_cvs_flag[Htid] is equal to 1, indicates         the number of elemental picture period intervals that the         decoded pictures of the current AU occupy for the display model.     -   When fixed_pic_rate_within_cvs_flag[Htid] is present and equal         to 1 and both general_nal_hrd_params_present_flag and         general_vcl_hrd_params_present_flag are equal to 0, the value of         pt_display_elemental_periods_minus1, if provided by external         means, shall be equal to 0.     -   When sps_field_seq_flag is equal to 1, the value of         pt_display_elemental_periods_minus1 shall be equal to 0.     -   When sps_field_seq_flag is equal to 0 and         fixed_pic_rate_within_cvs_flag[Htid] is equal to 1, a value of         pt_display_elemental_periods_minus1 greater than 0 could be used         to indicate a frame repetition period for displays that use a         fixed frame refresh interval equal to         DpbOutputElementalInterval[n] as given by the following equation         DpbOutputElementalInterval[n]=DpbOutputInterval[n]÷(pt_display_elemental_periods_minus1+1)     -   where DpbOutputInterval[n] is specified in the Equation below.

It should be noted that with respect to the semantics provided above, JVET-T2001 provides the following definitions:

-   -   access unit (AU): A set of PUs that belong to different layers         and contain coded pictures associated with the same time for         output from the DPB.     -   coded picture buffer (CPB): A first-in first-out buffer         containing DUs in decoding order specified in the hypothetical         reference decoder.     -   decoded picture buffer (DPB): A buffer holding decoded pictures         for reference, output reordering, or output delay specified for         the hypothetical reference decoder.     -   decoding unit (DU): An AU if DecodingUnitHrdFlag is equal to 0         or a subset of an AU otherwise, consisting of one or more VCL         NAL units in an AU and the associated non-VCL NAL units.     -   hypothetical reference decoder (HRD): A hypothetical decoder         model that specifies constraints on the variability of         conforming NAL unit streams or conforming byte streams that an         encoding process may produce.     -   picture unit (PU): A set of NAL units that are associated with         each other according to a specified classification rule, are         consecutive in decoding order, and contain exactly one coded         picture.

Further, it should be noted that JVET-T2001 provides the following with respect to picture output for a picture buffer:

-   -   The processes specified in this clause happen instantaneously at         the CPB removal time of AU n, AuCpbRemovalTime[n].     -   When picture n has PictureOutputFlag equal to 1, its DPB output         time DpbOutputTime[n] is derived as follows, where the variable         firstPicInBufferingPeriodFlag is equal to 1 if AU n is the first         AU of a BP and 0 otherwise:

if( !DecodingUnitHrdFlag ) {  DpbOutputTime[ n ] = AuCpbRemovalTime[ n ] + ClockTick * ( pt_dpb_output_delay −    AuDpbOutputDelta[ Htid ] )  if( firstPicInBufferingPeriodFlag )   DpbOutputTime[ n ] −= ClockTick * DpbDelayOffset } else  DpbOutputTime[ n ] = AuCpbRemovalTime[ n ] + ClockSubTick *  dpbOutputDuDelay

-   -   where AuDpbOutputDelta[Htid] is derived according to         pt_cpb_removal_delay_minus1[Htid] and         pt_cpb_removal_delay_delta_idx[Htid] in the PT SEI message         associated with AU n and         bp_cpb_removal_delay_delta_val[pt_cpb_removal_delay_delta_idx[Htid]         ] and bp_dpb_output_tid_offset[Htid] in the BP SEI message         associated with AU n, and dpbOutputDuDelay is the value of         dui_dpb_output_du_delay in the DUI SEI messages associated with         AU n when bp_du_dpb_params_in_pic_timing_sei_flag is equal to 0,         or the value of pt_dpb_output_du_delay in the PT SEI message         associated with AU n when         bp_du_dpb_params_in_pic_timing_sei_flag is equal top 1.         -   NOTE—When the syntax element dui_dpb_output_du_delay is not             present in any DUI SEI message associated with AU n, the             value is inferred to be equal to pt_dpb_output_du_delay in             the PT SEI message associated with AU n.     -   The output of the current picture is specified as follows:         -   If PictureOutputFlag is equal to 1 and DpbOutputTime[n] is             equal to AuCpbRemovalTime[n], the current picture is output.         -   Otherwise, if PictureOutputFlag is equal to 0, the current             picture is not output, but will be stored in the DPB as             specified.         -   Otherwise (PictureOutputFlag is equal to 1 and             DpbOutputTime[n] is greater than AuCpbRemovalTime[n]), the             current picture is output later and will be stored in the             DPB (as specified) and is output at time DpbOutputTime[n]             unless indicated not to be output by NoOutputOfPriorPicsFlag             equal to 1.     -   When output, the picture is cropped, using the conformance         cropping window for the picture.     -   When picture n is a picture that is output and is not the last         picture of the bitstream that is output, the value of the         variable DpbOutputInterval[n] is derived as follows:         DpbOutputInterval[n]=DpbOutputTime[nextPicInOutputOrder]−DpbOutputTime[n]     -   where nextPicInOutputOrder is the picture that follows picture n         in output order and has PictureOutputFlag equal to 1.

The signaling of buffer information in JVET-T2001 may be less than ideal. In particular, there are several cases where inference rules for syntax elements are undefined.

FIG. 1 is a block diagram illustrating an example of a system that may be configured to code (i.e., encode and/or decode) video data according to one or more techniques of this disclosure. System 100 represents an example of a system that may encapsulate video data according to one or more techniques of this disclosure. As illustrated in FIG. 1 , system 100 includes source device 102, communications medium 110, and destination device 120. In the example illustrated in FIG. 1 , source device 102 may include any device configured to encode video data and transmit encoded video data to communications medium 110. Destination device 120 may include any device configured to receive encoded video data via communications medium 110 and to decode encoded video data. Source device 102 and/or destination device 120 may include computing devices equipped for wired and/or wireless communications and may include, for example, set top boxes, digital video recorders, televisions, desktop, laptop or tablet computers, gaming consoles, medical imagining devices, and mobile devices, including, for example, smartphones, cellular telephones, personal gaming devices.

Communications medium 110 may include any combination of wireless and wired communication media, and/or storage devices. Communications medium 110 may include coaxial cables, fiber optic cables, twisted pair cables, wireless transmitters and receivers, routers, switches, repeaters, base stations, or any other equipment that may be useful to facilitate communications between various devices and sites. Communications medium 110 may include one or more networks. For example, communications medium 110 may include a network configured to enable access to the World Wide Web, for example, the Internet. A network may operate according to a combination of one or more telecommunication protocols. Telecommunications protocols may include proprietary aspects and/or may include standardized telecommunication protocols. Examples of standardized telecommunications protocols include Digital Video Broadcasting (DVB) standards, Advanced Television Systems Committee (ATSC) standards, Integrated Services Digital Broadcasting (ISDB) standards, Data Over Cable Service Interface Specification (DOCSIS) standards, Global System Mobile Communications (GSM) standards, code division multiple access (CDMA) standards, 3rd Generation Partnership Project (3GPP) standards, European Telecommunications Standards Institute (ETSI) standards, Internet Protocol (IP) standards, Wireless Application Protocol (WAP) standards, and Institute of Electrical and Electronics Engineers (IEEE) standards.

Storage devices may include any type of device or storage medium capable of storing data. A storage medium may include a tangible or non-transitory computer-readable media. A computer readable medium may include optical discs, flash memory, magnetic memory, or any other suitable digital storage media. In some examples, a memory device or portions thereof may be described as non-volatile memory and in other examples portions of memory devices may be described as volatile memory. Examples of volatile memories may include random access memories (RAM), dynamic random access memories (DRAM), and static random access memories (SRAM). Examples of non-volatile memories may include magnetic hard discs, optical discs, floppy discs, flash memories, or forms of electrically programmable memories (EPROM) or electrically erasable and programmable (EEPROM) memories. Storage device(s) may include memory cards (e.g., a Secure Digital (SD) memory card), internal/external hard disk drives, and/or internal/external solid state drives. Data may be stored on a storage device according to a defined file format.

FIG. 4 is a conceptual drawing illustrating an example of components that may be included in an implementation of system 100. In the example implementation illustrated in FIG. 4 , system 100 includes one or more computing devices 402A-402N, television service network 404, television service provider site 406, wide area network 408, local area network 410, and one or more content provider sites 412A-412N. The implementation illustrated in FIG. 4 represents an example of a system that may be configured to allow digital media content, such as, for example, a movie, a live sporting event, etc., and data and applications and media presentations associated therewith to be distributed to and accessed by a plurality of computing devices, such as computing devices 402A-402N. In the example illustrated in FIG. 4 , computing devices 402A-402N may include any device configured to receive data from one or more of television service network 404, wide area network 408, and/or local area network 410. For example, computing devices 402A-402N may be equipped for wired and/or wireless communications and may be configured to receive services through one or more data channels and may include televisions, including so-called smart televisions, set top boxes, and digital video recorders. Further, computing devices 402A-402N may include desktop, laptop, or tablet computers, gaming consoles, mobile devices, including, for example, “smart” phones, cellular telephones, and personal gaming devices.

Television service network 404 is an example of a network configured to enable digital media content, which may include television services, to be distributed. For example, television service network 404 may include public over-the-air television networks, public or subscription-based satellite television service provider networks, and public or subscription-based cable television provider networks and/or over the top or Internet service providers. It should be noted that although in some examples television service network 404 may primarily be used to enable television services to be provided, television service network 404 may also enable other types of data and services to be provided according to any combination of the telecommunication protocols described herein. Further, it should be noted that in some examples, television service network 404 may enable two-way communications between television service provider site 406 and one or more of computing devices 402A-402N. Television service network 404 may comprise any combination of wireless and/or wired communication media. Television service network 404 may include coaxial cables, fiber optic cables, twisted pair cables, wireless transmitters and receivers, routers, switches, repeaters, base stations, or any other equipment that may be useful to facilitate communications between various devices and sites. Television service network 404 may operate according to a combination of one or more telecommunication protocols. Telecommunications protocols may include proprietary aspects and/or may include standardized telecommunication protocols. Examples of standardized telecommunications protocols include DVB standards, ATSC standards, ISDB standards, DTMB standards, DMB standards, Data Over Cable Service Interface Specification (DOCSIS) standards, HbbTV standards, W3C standards, and UPnP standards.

Referring again to FIG. 4 , television service provider site 406 may be configured to distribute television service via television service network 404. For example, television service provider site 406 may include one or more broadcast stations, a cable television provider, or a satellite television provider, or an Internet-based television provider. For example, television service provider site 406 may be configured to receive a transmission including television programming through a satellite uplink/downlink. Further, as illustrated in FIG. 4 , television service provider site 406 may be in communication with wide area network 408 and may be configured to receive data from content provider sites 412A-412N. It should be noted that in some examples, television service provider site 406 may include a television studio and content may originate therefrom.

Wide area network 408 may include a packet based network and operate according to a combination of one or more telecommunication protocols. Telecommunications protocols may include proprietary aspects and/or may include standardized telecommunication protocols. Examples of standardized telecommunications protocols include Global System Mobile Communications (GSM) standards, code division multiple access (CDMA) standards, 3^(rd) Generation Partnership Project (3GPP) standards, European Telecommunications Standards Institute (ETSI) standards, European standards (EN), IP standards, Wireless Application Protocol (WAP) standards, and Institute of Electrical and Electronics Engineers (IEEE) standards, such as, for example, one or more of the IEEE 802 standards (e.g., Wi-Fi). Wide area network 408 may comprise any combination of wireless and/or wired communication media. Wide area network 408 may include coaxial cables, fiber optic cables, twisted pair cables, Ethernet cables, wireless transmitters and receivers, routers, switches, repeaters, base stations, or any other equipment that may be useful to facilitate communications between various devices and sites. In one example, wide area network 408 may include the Internet. Local area network 410 may include a packet based network and operate according to a combination of one or more telecommunication protocols. Local area network 410 may be distinguished from wide area network 408 based on levels of access and/or physical infrastructure. For example, local area network 410 may include a secure home network.

Referring again to FIG. 4 , content provider sites 412A-412N represent examples of sites that may provide multimedia content to television service provider site 406 and/or computing devices 402A-402N. For example, a content provider site may include a studio having one or more studio content servers configured to provide multimedia files and/or streams to television service provider site 406. In one example, content provider sites 412A-412N may be configured to provide multimedia content using the IP suite. For example, a content provider site may be configured to provide multimedia content to a receiver device according to Real Time Streaming Protocol (RTSP), HTTP, or the like. Further, content provider sites 412A-412N may be configured to provide data, including hypertext based content, and the like, to one or more of receiver devices computing devices 402A-402N and/or television service provider site 406 through wide area network 408. Content provider sites 412A-412N may include one or more web servers. Data provided by data provider site 412A-412N may be defined according to data formats.

Referring again to FIG. 1 , source device 102 includes video source 104, video encoder 106, data encapsulator 107, and interface 108. Video source 104 may include any device configured to capture and/or store video data. For example, video source 104 may include a video camera and a storage device operably coupled thereto. Video encoder 106 may include any device configured to receive video data and generate a compliant bitstream representing the video data. A compliant bitstream may refer to a bitstream that a video decoder can receive and reproduce video data therefrom. Aspects of a compliant bitstream may be defined according to a video coding standard. When generating a compliant bitstream video encoder 106 may compress video data. Compression may be lossy (discernible or indiscernible to a viewer) or lossless. FIG. 5 is a block diagram illustrating an example of video encoder 500 that may implement the techniques for encoding video data described herein. It should be noted that although example video encoder 500 is illustrated as having distinct functional blocks, such an illustration is for descriptive purposes and does not limit video encoder 500 and/or sub-components thereof to a particular hardware or software architecture. Functions of video encoder 500 may be realized using any combination of hardware, firmware, and/or software implementations.

Video encoder 500 may perform intra prediction coding and inter prediction coding of picture areas, and, as such, may be referred to as a hybrid video encoder. In the example illustrated in FIG. 5 , video encoder 500 receives source video blocks. In some examples, source video blocks may include areas of picture that has been divided according to a coding structure. For example, source video data may include macroblocks, CTUs, CBs, sub-divisions thereof, and/or another equivalent coding unit. In some examples, video encoder 500 may be configured to perform additional sub-divisions of source video blocks. It should be noted that the techniques described herein are generally applicable to video coding, regardless of how source video data is partitioned prior to and/or during encoding. In the example illustrated in FIG. 5 , video encoder 500 includes summer 502, transform coefficient generator 504, coefficient quantization unit 506, inverse quantization and transform coefficient processing unit 508, summer 510, intra prediction processing unit 512, inter prediction processing unit 514, filter unit 516, and entropy encoding unit 518. As illustrated in FIG. 5 , video encoder 500 receives source video blocks and outputs a bitstream.

In the example illustrated in FIG. 5 , video encoder 500 may generate residual data by subtracting a predictive video block from a source video block. The selection of a predictive video block is described in detail below. Summer 502 represents a component configured to perform this subtraction operation. In one example, the subtraction of video blocks occurs in the pixel domain. Transform coefficient generator 504 applies a transform, such as a discrete cosine transform (DCT), a discrete sine transform (DST), or a conceptually similar transform, to the residual block or sub-divisions thereof (e.g., four 8×8 transforms may be applied to a 16×16 array of residual values) to produce a set of residual transform coefficients. Transform coefficient generator 504 may be configured to perform any and all combinations of the transforms included in the family of discrete trigonometric transforms, including approximations thereof. Transform coefficient generator 504 may output transform coefficients to coefficient quantization unit 506. Coefficient quantization unit 506 may be configured to perform quantization of the transform coefficients. The quantization process may reduce the bit depth associated with some or all of the coefficients. The degree of quantization may alter the rate-distortion (i.e., bit-rate vs. quality of video) of encoded video data. The degree of quantization may be modified by adjusting a quantization parameter (QP). A quantization parameter may be determined based on slice level values and/or CU level values (e.g., CU delta QP values). QP data may include any data used to determine a QP for quantizing a particular set of transform coefficients. As illustrated in FIG. 5 , quantized transform coefficients (which may be referred to as level values) are output to inverse quantization and transform coefficient processing unit 508. Inverse quantization and transform coefficient processing unit 508 may be configured to apply an inverse quantization and an inverse transformation to generate reconstructed residual data. As illustrated in FIG. 5 , at summer 510, reconstructed residual data may be added to a predictive video block. In this manner, an encoded video block may be reconstructed and the resulting reconstructed video block may be used to evaluate the encoding quality for a given prediction, transformation, and/or quantization. Video encoder 500 may be configured to perform multiple coding passes (e.g., perform encoding while varying one or more of a prediction, transformation parameters, and quantization parameters). The rate-distortion of a bitstream or other system parameters may be optimized based on evaluation of reconstructed video blocks. Further, reconstructed video blocks may be stored and used as reference for predicting subsequent blocks.

Referring again to FIG. 5 , intra prediction processing unit 512 may be configured to select an intra prediction mode for a video block to be coded. Intra prediction processing unit 512 may be configured to evaluate a frame and determine an intra prediction mode to use to encode a current block. As described above, possible intra prediction modes may include planar prediction modes, DC prediction modes, and angular prediction modes. Further, it should be noted that in some examples, a prediction mode for a chroma component may be inferred from a prediction mode for a luma prediction mode. Intra prediction processing unit 512 may select an intra prediction mode after performing one or more coding passes. Further, in one example, intra prediction processing unit 512 may select a prediction mode based on a rate-distortion analysis. As illustrated in FIG. 5 , intra prediction processing unit 512 outputs intra prediction data (e.g., syntax elements) to entropy encoding unit 518 and transform coefficient generator 504. As described above, a transform performed on residual data may be mode dependent (e.g., a secondary transform matrix may be determined based on a prediction mode).

Referring again to FIG. 5 , inter prediction processing unit 514 may be configured to perform inter prediction coding for a current video block. Inter prediction processing unit 514 may be configured to receive source video blocks and calculate a motion vector for PUs of a video block. A motion vector may indicate the displacement of a prediction unit of a video block within a current video frame relative to a predictive block within a reference frame. Inter prediction coding may use one or more reference pictures. Further, motion prediction may be uni-predictive (use one motion vector) or bi-predictive (use two motion vectors). Inter prediction processing unit 514 may be configured to select a predictive block by calculating a pixel difference determined by, for example, sum of absolute difference (SAD), sum of square difference (SSD), or other difference metrics. As described above, a motion vector may be determined and specified according to motion vector prediction. Inter prediction processing unit 514 may be configured to perform motion vector prediction, as described above. Inter prediction processing unit 514 may be configured to generate a predictive block using the motion prediction data. For example, inter prediction processing unit 514 may locate a predictive video block within a frame buffer (not shown in FIG. 5 ). It should be noted that inter prediction processing unit 514 may further be configured to apply one or more interpolation filters to a reconstructed residual block to calculate sub-integer pixel values for use in motion estimation. Inter prediction processing unit 514 may output motion prediction data for a calculated motion vector to entropy encoding unit 518.

Referring again to FIG. 5 , filter unit 516 receives reconstructed video blocks and coding parameters and outputs modified reconstructed video data. Filter unit 516 may be configured to perform deblocking and/or Sample Adaptive Offset (SAO) filtering. SAO filtering is a non-linear amplitude mapping that may be used to improve reconstruction by adding an offset to reconstructed video data. It should be noted that as illustrated in FIG. 5 , intra prediction processing unit 512 and inter prediction processing unit 514 may receive modified reconstructed video block via filter unit 216. Entropy encoding unit 518 receives quantized transform coefficients and predictive syntax data (i.e., intra prediction data and motion prediction data). It should be noted that in some examples, coefficient quantization unit 506 may perform a scan of a matrix including quantized transform coefficients before the coefficients are output to entropy encoding unit 518. In other examples, entropy encoding unit 518 may perform a scan. Entropy encoding unit 518 may be configured to perform entropy encoding according to one or more of the techniques described herein. In this manner, video encoder 500 represents an example of a device configured to generate encoded video data according to one or more techniques of this disclosure.

Referring again to FIG. 1 , data encapsulator 107 may receive encoded video data and generate a compliant bitstream, e.g., a sequence of NAL units according to a defined data structure. A device receiving a compliant bitstream can reproduce video data therefrom. Further, as described above, sub-bitstream extraction may refer to a process where a device receiving a compliant bitstream forms a new compliant bitstream by discarding and/or modifying data in the received bitstream. It should be noted that the term conforming bitstream may be used in place of the term compliant bitstream. In one example, data encapsulator 107 may be configured to generate syntax according to one or more techniques described herein. It should be noted that data encapsulator 107 need not necessary be located in the same physical device as video encoder 106. For example, functions described as being performed by video encoder 106 and data encapsulator 107 may be distributed among devices illustrated in FIG. 4 .

As described above, the buffering information signaling in JVET-T2001 may be less than ideal. As provided above, for syntax element dui_dpb_output_du_delay, JVET-T2001 provides the following inference rule: When not present, the value of dui_dpb_output_du_delay is inferred to be equal to pt_dpb_output_du_delay. One condition under which dui_dpb_output_du_delay is not present is when bp_du_dpb_params_in_pic_timing_sei_flag is equal to 0 and dui_dpb_output_du_delay_present_flag is equal to 0. However, in this case, since bp_du_dpb_params_in_pic_timing_sei_flag is equal to 0, pt_dpb_output_du_delay is not present and it does not have an inference rule when not present. Thus, in this case pt_dpb_output_du_delay does not have a defined value and inferring dui_dpb_output_du_delay to be equal to pt_dpb_output_du_delay means dui_dpb_output_du_delay has undefined value. Further, it should be noted that in JVET-T2001, there is no constraint which disallows setting bp_du_dpb_params_in_pic_timing_sei_flag equal to 0 and dui_dpb_output_du_delay equal to 0 in DUI SEI for each DU of an AU.

It is asserted that an efficient design for the decoding unit information SEI message should allow that when bp_du_dpb_params_in_pic_timing_sei_flag is equal to 0, the syntax element dui_dpb_output_du_delay may be signaled in one or more DU information SEI messages for one or more DUs of an AU. This provides bit savings by not requiring signaling dui_dpb_output_du_delay in each decoding unit information SEI message. For example, the dui_dpb_output_du_delay may only be signaled in the last DU of the AU and thus the value of dui_dpb_output_du_delay_present_flag is set to 1 for the last DUI SEI and is set to 0 for the other DUI SEIs for the AU. It is asserted that in JVET-T2001, the value of dui_dpb_output_du_delay is used to set the value of dpbOutputDuDelay when bp_du_dpb_params_in_pic_timing_sei_flag is equal to 0 and is used for the operation of HRD. Thus, dui_dpb_output_du_delay needs to have a defined value.

Thus, in one example, according to the techniques herein the semantics of syntax elements dui_dpb_output_du_delay and dui_dpb_output_du_delay_present_flag may be based on the following:

-   -   dui_dpb_output_du_delay is used to compute the DPB output time         of the AU when DecodingUnitHrdFlag is equal to 1 and         bp_du_dpb_params_in_pic_timing_sei_flag is equal to 0. It         specifies how many sub clock ticks to wait after removal of the         last DU in an AU from the CPB before the decoded pictures of the         AU are output from the DPB. When not present and when         bp_du_dpb_params_in_pic_timing_sei_flag is equal to 0, the value         of dui_dpb_output_du_delay is inferred to be equal to         dui_dpb_output_du_delay from any DU belonging to the same AU for         which dui_dpb_output_du_delay_present_flag is equal to 1. The         length of the syntax element dui_dpb_output_du_delay is given in         bits by bp_dpb_output_delay_du_length_minus1+1.     -   dui_dpb_output_du_delay_present_flag equal to 1 specifies the         presence of the dui_dpb_output_du_delay syntax element in the         DUI SEI message. dui_dpb_output_du_delay_present_flag equal to 0         specifies the absence of the dui_dpb_output_du_delay syntax         element in the DUI SEI message. When not present, the value of         dui_dpb_output_du_delay_present_flag is inferred to be equal to         0.     -   When bp_du_dpb_params_in_pic_timing_sei_flag is equal to 0, at         least one DUI SEI message associated with the DUs of an AU shall         have dui_dpb_output_du_delay_present_flag equal to 1.     -   Or in other words:     -   When bp_du_dpb_params_in_pic_timing_sei_flag is equal to 0, at         least one DUI SEI message associated with the DUs of an AU shall         have the syntax element dui_dpb_output_du_delay signalled.     -   Or in other words:     -   When bp_du_dpb_params_in_pic_timing_sei_flag is equal to 0, at         least one DUI SEI message associated with the DUs of an AU shall         have the syntax element dui_dpb_output_du_delay present.     -   Further, in this example, the note “When the syntax element         dui_dpb_output_du_delay is not present in any DUI SEI message         associated with AU n, the value is inferred to be equal to         pt_dpb_output_du_delay in the PT SEI message associated with AU         n” is removed from the picture output process specified in         JVET-T2001.

It should be noted that, according to the techniques herein, the inferences rule for syntax element dui_dpb_output_du_delay provided above may be specified as follows:

-   -   dui_dpb_output_du_delay is used to compute the DPB output time         of the AU when DecodingUnitHrdFlag is equal to 1 and         bp_du_dpb_params_in_pic_timing_sei_flag is equal to 0. It         specifies how many sub clock ticks to wait after removal of the         last DU in an AU from the CPB before the decoded pictures of the         AU are output from the DPB. When         bp_du_dpb_params_in_pic_timing_sei_flag is equal to 0 and         dui_dpb_output_du_delay_present_flag is equal to 0, the value of         dui_dpb_output_du_delay is inferred to be equal to         dui_dpb_output_du_delay from any DU belonging to the same AU for         which dui_dpb_output_du_delay_present_flag is equal to 1. The         length of the syntax element dui_dpb_output_du_delay is given in         bits by bp_dpb_output_delay_du_length_minus1+1.     -   Or as:     -   dui_dpb_output_du_delay is used to compute the DPB output time         of the AU when DecodingUnitHrdFlag is equal to 1 and         bp_du_dpb_params_in_pic_timing_sei_flag is equal to 0. It         specifies how many sub clock ticks to wait after removal of the         last DU in an AU from the CPB before the decoded pictures of the         AU are output from the DPB. When not present, the value of         dui_dpb_output_du_delay is inferred as follows:     -   If bp_du_dpb_params_in_pic_timing_sei_flag equal to 0 and         dui_dpb_output_du_delay_present_flag is equal to 0,         dui_dpb_output_du_delay is inferred to be equal to         dui_dpb_output_du_delay from any DU belonging to the same AU for         which bp_du_dpb_params_in_pic_timing_sei_flag equal to 0 and         dui_dpb_output_du_delay_present_flag is equal to 1.     -   Otherwise dui_dpb_output_du_delay is inferred to be equal to         pt_dpb_output_du_delay.     -   Or as:     -   dui_dpb_output_du_delay is used to compute the DPB output time         of the AU when DecodingUnitHrdFlag is equal to 1 and         bp_du_dpb_params_in_pic_timing_sei_flag is equal to 0. It         specifies how many sub clock ticks to wait after removal of the         last DU in an AU from the CPB before the decoded pictures of the         AU are output from the DPB. When not present, the value of         dui_dpb_output_du_delay is inferred to be equal to         dui_dpb_output_du_delay from any DU belonging to the same AU for         which dui_dpb_output_du_delay_present_flag is equal to 1.     -   Or as:     -   dui_dpb_output_du_delay is used to compute the DPB output time         of the AU when DecodingUnitHrdFlag is equal to 1 and         bp_du_dpb_params_in_pic_timing_sei_flag is equal to 0. It         specifies how many sub clock ticks to wait after removal of the         last DU in an AU from the CPB before the decoded pictures of the         AU are output from the DPB. When not present, the value of         dui_dpb_output_du_delay is inferred to be equal to         pt_dpb_output_du_delay when         bp_du_dpb_params_in_pic_timing_sei_flag is equal to 1.

In another example, it may be required that dui_dpb_output_du_delay is signalled in each DUI SEI message when bp_du_dpb_params_in_pic_timing_sei_flag is equal to 0, which may be specified in semantics as:

-   -   If bp_du_dpb_params_in_pic_timing_sei_flag is equal to 0,         dui_dpb_output_du_delay_present_flag shall be equal to 1.

Further, the following additional condition may be added as a bitstream conformance requirement:

-   -   It is a requirement of bitstream conformance that all DUI SEI         messages that are associated with the same AU, apply to the same         operation point, and have         bp_du_dpb_params_in_pic_timing_sei_flag equal to 0 and         dui_dpb_output_du_delay_present_flag equal to 1 shall have the         same value of dui_dpb_output_du_delay.

Further, in one example, according to the techniques herein, a picture output process may be based on the following:

-   -   The processes specified in this clause happen instantaneously at         the CPB removal time of AU n, AuCpbRemovalTime[n].     -   When picture n has PictureOutputFlag equal to 1, its DPB output         time DpbOutputTime[n] is derived as follows, where the variable         firstPicInBufferingPeriodFlag is equal to 1 if AU n is the first         AU of a BP and 0 otherwise:         -   if (!DecodingUnitHrdFlag) {             -   DpbOutputTime[n]=AuCpbRemovalTime[n]+ClockTick*(pt_dpb_output_delay−AuDpbOutputDelta[Htid])             -   if (firstPicInBufferingPeriodFlag)                 -   DpbOutputTime[n]-=ClockTick*DpbDelayOffset         -   } else             -   DpbOutputTime[n]=AuCpbRemovalTime[n]+ClockSubTick*dpbOutputDuDelay                 where AuDpbOutputDelta[Htid] is derived according to                 pt_cpb_removal_delay_minus1[Htid] and                 pt_cpb_removal_delay_delta_idx[Htid] in the PT SEI                 message associated with AU n and                 bp_cpb_removal_delay_delta_val[pt_cpb_removal_delay_delta_idx[Htid]                 ] and bp_dpb_output_tid_offset[Htid] in the BP SEI                 message associated with AU n, and dpbOutputDuDelay is                 the value of dui_dpb_output_du_delay in the DUI SEI                 message associated with AU n when                 bp_du_dpb_params_in_pic_timing_sei_flag is equal to 0                 and dui_dpb_output_du_delay_present_flag is equal to 1,                 or the value of pt_dpb_output_du_delay in the PT SEI                 message associated with AU n when                 bp_du_dpb_params_in_pic_timing_sei_flag is equal top 1.     -   The output of the current picture is specified as follows:         -   If PictureOutputFlag is equal to 1 and DpbOutputTime[n] is             equal to AuCpbRemovalTime[n], the current picture is output.         -   Otherwise, if PictureOutputFlag is equal to 0, the current             picture is not output, but will be stored in the DPB as             specified.         -   Otherwise (PictureOutputFlag is equal to 1 and             DpbOutputTime[n] is greater than AuCpbRemovalTime[n]), the             current picture is output later and will be stored in the             DPB (as specified) and is output at time DpbOutputTime[n]             unless indicated not to be output by NoOutputOfPriorPicsFlag             equal to 1.     -   When output, the picture is cropped, using the conformance         cropping window for the picture.     -   When picture n is a picture that is output and is not the last         picture of the bitstream that is output, the value of the         variable DpbOutputInterval[n] is derived as follows:         DpbOutputInterval[n]=DpbOutputTime[nextPicInOutputOrder]−DpbOutputTime[n]     -   where nextPicInOutputOrder is the picture that follows picture n         in output order and has PictureOutputFlag equal to 1.

Further, it should be noted that according to the techniques herein, the term AU may be replaced with the term PU in some cases.

In this manner, source device 102 represents an example of a device configured to signal decoding unit information messages for decoding units in the same access unit, signal an instance of a syntax element used to compute a decoded picture buffer output time in at least one of the decoding unit information messages, and not signal an instance of the syntax element used to compute a decoded picture buffer output time in at least one of the decoding unit information messages, where when not present, the value of the syntax element is inferred to be equal to a corresponding instance of the syntax element from any decoding unit belonging to the same access unit.

Referring again to FIG. 1 , interface 108 may include any device configured to receive data generated by data encapsulator 107 and transmit and/or store the data to a communications medium. Interface 108 may include a network interface card, such as an Ethernet card, and may include an optical transceiver, a radio frequency transceiver, or any other type of device that can send and/or receive information. Further, interface 108 may include a computer system interface that may enable a file to be stored on a storage device. For example, interface 108 may include a chipset supporting Peripheral Component Interconnect (PCI) and Peripheral Component Interconnect Express (PCIe) bus protocols, proprietary bus protocols, Universal Serial Bus (USB) protocols, I²C, or any other logical and physical structure that may be used to interconnect peer devices.

Referring again to FIG. 1 , destination device 120 includes interface 122, data decapsulator 123, video decoder 124, and display 126. Interface 122 may include any device configured to receive data from a communications medium. Interface 122 may include a network interface card, such as an Ethernet card, and may include an optical transceiver, a radio frequency transceiver, or any other type of device that can receive and/or send information. Further, interface 122 may include a computer system interface enabling a compliant video bitstream to be retrieved from a storage device. For example, interface 122 may include a chipset supporting PCI and PCIe bus protocols, proprietary bus protocols, USB protocols, I²C, or any other logical and physical structure that may be used to interconnect peer devices. Data decapsulator 123 may be configured to receive and parse any of the example syntax structures described herein.

Video decoder 124 may include any device configured to receive a bitstream (e.g., a sub-bitstream extraction) and/or acceptable variations thereof and reproduce video data therefrom. Display 126 may include any device configured to display video data. Display 126 may comprise one of a variety of display devices such as a liquid crystal display (LCD), a plasma display, an organic light emitting diode (OLED) display, or another type of display. Display 126 may include a High Definition display or an Ultra High Definition display. It should be noted that although in the example illustrated in FIG. 1 , video decoder 124 is described as outputting data to display 126, video decoder 124 may be configured to output video data to various types of devices and/or sub-components thereof. For example, video decoder 124 may be configured to output video data to any communication medium, as described herein.

FIG. 6 is a block diagram illustrating an example of a video decoder that may be configured to decode video data according to one or more techniques of this disclosure (e.g., the decoding process for reference-picture list construction described above). In one example, video decoder 600 may be configured to decode transform data and reconstruct residual data from transform coefficients based on decoded transform data. Video decoder 600 may be configured to perform intra prediction decoding and inter prediction decoding and, as such, may be referred to as a hybrid decoder. Video decoder 600 may be configured to parse any combination of the syntax elements described above in Tables 1-5. Video decoder 600 may decode a picture based on or according to the processes described above, and further based on parsed values in Tables 1-5.

In the example illustrated in FIG. 6 , video decoder 600 includes an entropy decoding unit 602, inverse quantization unit 604, transform coefficient processing unit 606, intra prediction processing unit 608, inter prediction processing unit 610, summer 612, post filter unit 614, and reference buffer 616. Video decoder 600 may be configured to decode video data in a manner consistent with a video coding system. It should be noted that although example video decoder 600 is illustrated as having distinct functional blocks, such an illustration is for descriptive purposes and does not limit video decoder 600 and/or sub-components thereof to a particular hardware or software architecture. Functions of video decoder 600 may be realized using any combination of hardware, firmware, and/or software implementations.

As illustrated in FIG. 6 , entropy decoding unit 602 receives an entropy encoded bitstream. Entropy decoding unit 602 may be configured to decode syntax elements and quantized coefficients from the bitstream according to a process reciprocal to an entropy encoding process. Entropy decoding unit 602 may be configured to perform entropy decoding according any of the entropy coding techniques described above. Entropy decoding unit 602 may determine values for syntax elements in an encoded bitstream in a manner consistent with a video coding standard. As illustrated in FIG. 6 , entropy decoding unit 602 may determine a quantization parameter, quantized coefficient values, transform data, and prediction data from a bitstream. In the example illustrated in FIG. 6 , inverse quantization unit 604 and inverse transform coefficient processing unit 606 receive quantized coefficient values from entropy decoding unit 602 and output reconstructed residual data.

Referring again to FIG. 6 , reconstructed residual data may be provided to summer 612. Summer 612 may add reconstructed residual data to a predictive video block and generate reconstructed video data. A predictive video block may be determined according to a predictive video technique (i.e., intra prediction and inter frame prediction). Intra prediction processing unit 608 may be configured to receive intra prediction syntax elements and retrieve a predictive video block from reference buffer 616. Reference buffer 616 may include a memory device configured to store one or more frames of video data. Intra prediction syntax elements may identify an intra prediction mode, such as the intra prediction modes described above. Inter prediction processing unit 610 may receive inter prediction syntax elements and generate motion vectors to identify a prediction block in one or more reference frames stored in reference buffer 616. Inter prediction processing unit 610 may produce motion compensated blocks, possibly performing interpolation based on interpolation filters. Identifiers for interpolation filters to be used for motion estimation with sub-pixel precision may be included in the syntax elements. Inter prediction processing unit 610 may use interpolation filters to calculate interpolated values for sub-integer pixels of a reference block. Post filter unit 614 may be configured to perform filtering on reconstructed video data. For example, post filter unit 614 may be configured to perform deblocking and/or Sample Adaptive Offset (SAO) filtering, e.g., based on parameters specified in a bitstream. Further, it should be noted that in some examples, post filter unit 614 may be configured to perform proprietary discretionary filtering (e.g., visual enhancements, such as, mosquito noise reduction). As illustrated in FIG. 6 , a reconstructed video block may be output by video decoder 600. In this manner, video decoder 600 represents an example of a device configured to receive a decoding unit information message, determine a syntax element used to compute a decoded picture buffer output time is not present in the decoding unit information message, and infer the value of the syntax element used to compute a decoded picture buffer output time to be equal to a corresponding instance of the syntax element from any decoding unit belonging to the same access unit.

In one or more examples, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium and executed by a hardware-based processing unit. Computer-readable media may include computer-readable storage media, which corresponds to a tangible medium such as data storage media, or communication media including any medium that facilitates transfer of a computer program from one place to another, e.g., according to a communication protocol. In this manner, computer-readable media generally may correspond to (1) tangible computer-readable storage media which is non-transitory or (2) a communication medium such as a signal or carrier wave. Data storage media may be any available media that can be accessed by one or more computers or one or more processors to retrieve instructions, code and/or data structures for implementation of the techniques described in this disclosure. A computer program product may include a computer-readable medium.

By way of example, and not limitation, such computer-readable storage media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage, or other magnetic storage devices, flash memory, or any other medium that can be used to store desired program code in the form of instructions or data structures and that can be accessed by a computer. Also, any connection is properly termed a computer-readable medium. For example, if instructions are transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium. It should be understood, however, that computer-readable storage media and data storage media do not include connections, carrier waves, signals, or other transitory media, but are instead directed to non-transitory, tangible storage media. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and Blu-ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media.

Instructions may be executed by one or more processors, such as one or more digital signal processors (DSPs), general purpose microprocessors, application specific integrated circuits (ASICs), field programmable logic arrays (FPGAs), or other equivalent integrated or discrete logic circuitry. Accordingly, the term “processor,” as used herein may refer to any of the foregoing structure or any other structure suitable for implementation of the techniques described herein. In addition, in some aspects, the functionality described herein may be provided within dedicated hardware and/or software modules configured for encoding and decoding, or incorporated in a combined codec. Also, the techniques could be fully implemented in one or more circuits or logic elements.

The techniques of this disclosure may be implemented in a wide variety of devices or apparatuses, including a wireless handset, an integrated circuit (IC) or a set of ICs (e.g., a chip set). Various components, modules, or units are described in this disclosure to emphasize functional aspects of devices configured to perform the disclosed techniques, but do not necessarily require realization by different hardware units. Rather, as described above, various units may be combined in a codec hardware unit or provided by a collection of interoperative hardware units, including one or more processors as described above, in conjunction with suitable software and/or firmware.

Moreover, each functional block or various features of the base station device and the terminal device used in each of the aforementioned embodiments may be implemented or executed by a circuitry, which is typically an integrated circuit or a plurality of integrated circuits. The circuitry designed to execute the functions described in the present specification may comprise a general-purpose processor, a digital signal processor (DSP), an application specific or general application integrated circuit (ASIC), a field programmable gate array (FPGA), or other programmable logic devices, discrete gates or transistor logic, or a discrete hardware component, or a combination thereof. The general-purpose processor may be a microprocessor, or alternatively, the processor may be a conventional processor, a controller, a microcontroller or a state machine. The general-purpose processor or each circuit described above may be configured by a digital circuit or may be configured by an analogue circuit. Further, when a technology of making into an integrated circuit superseding integrated circuits at the present time appears due to advancement of a semiconductor technology, the integrated circuit by this technology is also able to be used.

Various examples have been described. These and other examples are within the scope of the following claims. 

What is claimed is:
 1. A method of decoding video data, the method comprising: receiving a first decoding unit information message corresponding to a first decoding unit of a current access unit; determining whether or not a decoding unit information (DUI) decoded picture buffer (DPB) output decoding unit (DU) delay syntax element used to compute a decoded picture buffer output time of the current access unit is present in the first decoding unit information message; and based on the DUI DPB output DU delay syntax element not being present in the first decoding unit information message and decoding unit level decoded picture buffer output delay parameters being present in the first decoding unit information message and not in picture timing information messages, inferring a value of the DUI DPB output DU delay syntax element to be equal to a value of a corresponding instance of the DUI DPB output DU delay syntax element present in a second decoding unit information message, wherein the second decoding unit information message corresponds to a second decoding unit of the current access unit.
 2. A device comprising one or more processors configured to: receive a first decoding unit information message corresponding to a first decoding unit of a current access unit; determine whether or not a decoding unit information (DUI) decoded picture buffer (DPB) output decoding unit (DU) delay syntax element used to compute a decoded picture buffer output time of the current access unit is present in the first decoding unit information message; and based on the DUI DPB output DU delay syntax element not being present in the first decoding unit information message and decoding unit level decoded picture buffer output delay parameters being present in the first decoding unit information message and not in picture timing information messages, infer a value of the DUI DPB output DU delay syntax element to be equal to a value of a corresponding instance of the DUI DPB output DU delay syntax element present in a second decoding unit information message, wherein the second decoding unit information message corresponds to a second decoding unit of the current access unit.
 3. The device of claim 2, wherein the device includes a video decoder.
 4. A non-transitory computer-readable storage medium of a device storing one or more instructions that, when executed by one or more processors of the device, cause the one or more processors of the device to: receive a first decoding unit information message corresponding to a first decoding unit of a current access unit; determine whether or not a decoding unit information (DUI) decoded picture buffer (DPB) output decoding unit (DU) delay syntax element used to compute a decoded picture buffer output time of the current access unit is present in the first decoding unit information message; and based on the DUI DPB output DU delay syntax element not being present in the first decoding unit information message and decoding unit level decoded picture buffer output delay parameters being present in the first decoding unit information message and not in picture timing information messages, infer a value of the DUI DPB output DU delay syntax element to be equal to a value of a corresponding instance of the DUI DPB output DU delay syntax element present in a second decoding unit information message, wherein the second decoding unit information message corresponds to a second decoding unit of the current access unit. 